I try to take into account just about everything.

Economy-
I'm big into making money. If you're on a very progressed server, your blues and blue equipment mats aren't going to sell well for very much longer.

Progression-
WoWProgress can tell you this very easily. My main's server is Blackrock (I've been there forever, don't say gtfo). Trade is constantly filled with LFM <whatever raid here>, and people looking to progress their specific tradeskill. The downside of a realm of high population and intense progression are players with a very elitist attitude. Additionally, hour long queues are prevalent and dissuade many.

Population-
As stated above, high populations are good and bad. You don't want your 1g buyout stack of truegold to sit on the AH for 48 hours because no one is around to see it, but you don't want to be on a locked server. Unfortunately, we're at the start of an expansion. It's hard to gauge what a server's population will end up staying at.

Annoying people-

I have some alts on Ghostlands. Ghostlands ended up becoming a very populated server and are about 1:1 horde and alliance. Unfortunately, progression never thrived. Progression plateaued at about 4/12 ICC10. Because of all of the bads, the denizens of Ghostlands had to find a new outlet for their energy. The victim of this was trade chat and the forums. A few of the more energetic of people made names for themselves as "popular." Many of these people post irrelevant threads about themselves on the forums and discuss unimportant things there. Thankfully, they make themselves easy to spot from a player looking to transfer and reroll. When WoWProgress and WoWCensus can't give me the answer I need, I look to the forums and when I see these types of people, I know that this probably isn't a good realm. These people would be pushed aside and ignored by players on realms with a more progression/pvp oriented culture.


To end, I'd look at a pvp server (my preference) with a higher population with your given faction. Look for higher progression with the tools listed above. Make a level 1 and run to the main city and scope things out.