I think it really depends on what faction you play and what your favorite thing is, PvE or PvP.
If you are alliance and PvE is your thing, Silvermoon(PvE realm) is a good choice.
Its only a medium populated, but the alliance people there are very active. I have a level 62 character and there is a lot of dungeon activity.
Has a rather small horde player base.
If you are horde and PvE is what you want, I'd suggest Magtheridon(PvP realm). I'll probably get a lot of flak for saying that, but I think its true.
It is a PvP realm, but the horde has like 93% of the player base, so it pretty much feels like a PvE realm.
I have an old horde character, but haven't played it since WotLK released, so it might have changed, but doubt it.
If you play alliance, then you'll have your work cut out.
You'll have to listen to a lot of Ensidia fan talk there thou.
If you like fair numbers and want the occasional world PvP, with a sidedish of PvE, then Stormscale(PvP realm) is a great server.
I believe it has a good even number of horde and alliance players and it is a very active server.
The horde players seems to be a bit more aggressive when it comes to ganking people. I play alliance there, so might be a bit biased.
