Picking a Server
There are a few things to keep in mind when you pick a server to play on.
Where are Your Friends Playing?
With each character your create, you can only interact fully with people on the same server (realm) and faction (Horde vs Alliance) as your character. You can create characters on different servers if you like, but then they cannot support each other by e.g. swapping gear, money, supplies or mailing items to each other, etc.
You are allowed limited access to other servers. There is, however, the possibility of paid transfers. For a fee, you may move one character to another server. The character will be unplayable while the transfer occurs, and a character can only be moved once every month. That is to say, if Alice was moved, she cannot be moved again for a month, but your second character ("alt"), Bob, can.
Other than that, the only way for people on different servers to meet is through the cross-realm PVP battlegrounds, where characters from servers in the same battlegroup can meet. However, there is no guarantee that two players who would like to interact will be put into the same battleground game. In addition, cross-realm instance grouping is possible within a battlegroup. Cross-realm chat, while announced by Blizzard, is not yet in the live game.
What's Your Time Zone?
Playing on a server with a time zone similar to the one you live in means more people will be on around the time you're going to play — assuming you play during peak hours, which varies but is usually between 6 p.m. and 10 p.m. on the server during weekdays. This affects the game in several ways, some of which might not be immediately apparent or affect you until you reach higher levels.
Your realm's time zone can affect your World of Warcraft experience in following ways, among others:
- The number of people who are available for you to group with. This is critical for instanced dungeons, and if you are interested in endgame you may find that this is your most important consideration as you will want to be active around the same time that the people in your guild are raiding.
- The amount of buying and selling that is going on and the prices in the auction house at peak hours.
- The amount of competition for resources that are out in the wild. The more people playing, the more might be looking for the same herb or quest mob that you're looking for.
- The number of opposite faction players who are around to attack you (especially if you are playing on a PVP server).
- The amount of activity going on in Battlegrounds. (Note that since the introduction of Battlegroups this has become a much smaller consideration.)
People who are usually unable to play during peak hours often try to play on a realm in a different time zone than the one they live in. If you tend to be available earlier than peak hours, you might want to look for a server that is in a time zone earlier than where you live. Similarly, if you tend to be available later than peak hours, you might want to look for a realm that is in a time zone later than where you live. This will generally maximize the number of people who are around when you are also looking to play.
Which Language Do You Prefer to Speak In?
The European Realms are divided up by which language is primarily spoken on them. No rules exist that ban you from speaking other languages on the servers, but you may feel more comfortable on a server where the majority of players speak a language that you understand.
What's the Server Population?
Each realm has a population listed on the server selection screen. Each realm is characterized as having Recommended, Low, Medium, High, and Full population. Recommended servers are what 
[Blizzard] thinks will give a new player the best experience, while the rest are categorized based on how many players are currently logged into the realm. These servers change throughout the day, so you may want to decide on a server at the time you would normally play, so that you'll know how full it is normally. You cannot create a character on a Full server unless you already have characters there. Some High population servers have wait queues during peak hours. This means you cannot sign in at all to them until other people have completely logged off of that server.
Each type of realm has benefits and drawbacks for new players.
- Realms that are usually at "Low" population are often very welcoming of new players. The lower population means that there is a great deal of demand for new players on the realm, and experienced players will often be more willing and helpful in bringing a newer player up to speed than on other realms and may have more patience with new players in general. However, the realm's Auction House will probably not have a very wide selection of items available to buy and it may be challenging to find players to group with. There will probably never be a need to wait in queue to log into these realms.
- Realms that are usually at "Medium" populations offer a compromise between extremes. Not much, if any demand, exists on these realms for new players, although they are usually not disliked either. These realms usually have a wide variety of items on their Auction House and finding other players to group with will not usually be a problem. Even at peak hours there is seldom if ever a queue to log into these servers.
- Realms that are usually at "High" populations can be rather discouraging of newer players (and not just those who are inexperienced with World of Warcraft). These realms sometimes have queue times to log in that can range from a few minutes to an hour or more. While the Auction House is often full of items and there are usually a lot of other players looking for people to group with, be in mind that with a larger group of people there are can often be a corresponding increase the number of players who behave badly toward others or are outright unpleasant to deal with, something that on Low and Medium population realms are at a relative minimum (though hardly non-existent). On a High-population server, a player looking to act negatively toward other players will probably be able to find other like-minded individuals, and even find entire guilds devoted to this sort of behavior.
- Realms that are often at "Full" populations are much like realms at "High" populations, but even more so. Players on these realms may be outright hostile to new players regardless of their experience with World of Warcraft, as login queues on these realms may regularly last hours. However, if you are able to log in, the Auction House will be full of items and there will be a vast number of players who you may be able to group with.
Blizzard occasionally releases new realms so that players can experience World of Warcraft on a completely new server. New servers, instead of displaying population, display the "New" status. New status means the server has just recently been put online and characters will be lower levels on average and the population of course starts very low. This generally means less resource competition and also a small economy so trading at the auction house will be reduced and prices will usually be lower.
When these new servers are populated, everyone starts at level 1, but after a month or two there will be many hardcore players at the level cap and endgame will begin to pick up from there. Down the road, there is also the possibility of entire high level guilds transferring onto the server, giving it a kick start. However, players may not pay to transfer to servers flagged as New for six months.
What is the Horde/Alliance Breakdown?
In some servers the ratio of the members of each faction is uneven. On some servers, there are more Alliance than Horde, while other times it can be a complete opposite, or even an evenly-matched ratio. Imbalances in factions can be an issue for PVP, grouping up, or just trying to complete quests since sometimes you have to wait for quests to respawn. Sites like WarcraftRealms.com show you the horde/alliance breakdown and other useful information (e.g. how many horde players are online at 9pm) connected with choosing a realm. However, because these sites don't have access to official population numbers and rely on largely on player reporting (via add-ons), they are widely regarded (including by Blizzard) as inaccurate. Blizzard does not publish official numbers, but its representatives have commented several times that the numbers on population-measurement sites like WarcraftRealms.com sometimes have little relationship to the actual active population.
Some say that one reason for the Alliance bias is the argument that the Alliance quests and areas are more polished than the Horde quests/areas. Other than that, some choose to play characters that are more appealing to the eye, or more similar to traditional heroes of fantasy literature and games. However, there are some arguments for the Horde as well. Some argue - based on little more than personal opinion - that the Horde player base is more mature than the Alliance player base. Others like the wide diversity of races in the faction. From there, the choice between Alliance and Horde would obviously depend on taste. See Races for more information on each.
What Kind of Experience Are You Looking For?
This is probably the biggest choice you have to make while playing World of Warcraft. There are four types of servers.
- PVE (Normal)
- These servers pit player versus the environment; on a PVE server, you cannot be attacked by another player (with certain very small and specific exceptions) unless you take an action to flag yourself for PVP. This may be the least stressful gaming experience especially if you are new to the game, because of this it may be good idea for your first realm to be in a normal server so you can learn how to play as well as enjoy the story of the game. You can PVP if you want, but you are not required to. On these servers, most PVP takes place inside the Battlegrounds and Arena, but can also take place anywhere else. Attendance to the battlegrounds is completely optional, as is any other PVP experience.
- It is worth noting that PVE servers are stigmatized as "easy mode" by those who believe that PVP is the only correct way to play the game. This includes use of the derisive term carebear for players who choose to play on PVE servers.
- PVP (Player vs. Player)
- Player vs. player realms are identical to PVE realms in the various races' starting areas (the level 1-10 zones, such as Elwynn Forest or Durotar). However, outside of those areas, players are automatically flagged for PVP combat, and can be killed by an opposite-faction player at any time. Many players believe that PVP is required in order to have a truly fulfilling experience in World of Warcraft. Factions are more tightly knit and PVP lends more of a sense of immediate conflict between the factions (as hardcore PVPers are fond of saying, "it is World of Warcraft, after all"). However, a PVP server can be much more stressful and frustrating to play on than a PVE server, due to the constant risk of being attacked even in areas that seem safe. In addition, since there are no penalties or punishments for killing player characters who are lower level than you are, PVP servers attract players who enjoy leveling characters to the level cap and then harassing much lower-level characters, who have no way of defending themselves save calling in higher-level friends or switching to their level-capped character. Since this isn't possible for players new to the game or to the server, PVP servers are not recommended as starting servers unless a player is willing to deal with that kind of harassment.
- Until very recently, players on PVP servers were limited to characters from a single faction on that server. In other words, if your first character on the server was a Horde character, all the rest of your characters on that server had to be Horde, unless you deleted all of them and started over with a blank slate. However, recent changes allow players to make characters from both factions on PVP servers; also, character transfers from PVE to PVP servers were recently opened up, allowing players to level to the level cap in relative safety and then transfer to a PVP server to participate in the worldwide combat.
- RP (Role Playing)
- "RP" is a meta-category for servers; there are both RP-PVE and RP-PVP servers. If you are more interested in being immersed in the game world than leveling up or getting cool items, these servers are for you. In these servers, you don't have a character to power-level. You are the character. People accept you if you talk like your character (with whatever accent, whatever vocabulary), and you're also able to act like your character. In this server you also don't have to worry about PVP since you can only be killed by other faction players if you so choose (like PVE servers). You are much less likely to get griefers on this server. Also, character name rules are stricter and out of character speech on public channels or in /say or /yell can earn you a visit from a GM who will require you to behave, etc.
- RP-PVP (Role Playing Player vs. Player)
- The newest type of server, RP-PVP servers have the elements of all-out PVP combat, but with the constraints of the RP ruleset. This is the type of server to choose if you are interested in being able to act out a character as truly as possible, by having him/her being able to attack members of the other faction at any time.