I was playing on Firemaw at the start, but the queues made me switch over to High populated server and I chose Dreadmist.
I am also playing on Skullflame (which is High as well) with my Paladin alt and high populated realms imo are the best - no queues (if there are any in the future, they won't be long), auction house is alive and you can find dungeons with no problems.
Don't want to play on Full anymore. Queues are not fun when you wait the whole day at work to get to play and in the end you just sit at the login screen. :(