probably in the order of frequency that I've been playing lately...
Absolute, Titan, JetSet, Pokerstars, UltimateBet, FullTilt. I've never deposited on any of them...I either play freerolls, fun games, or play what I've won on freerolls.
FullTilt's biggest weakness (IMHO) is that they have VERY few freerolls. The advantage is, I can play a play money sit 'n go with my wife. Other sites, we can't both access at the same time (I can understand that in real money games, but play money???). Full Tilt lets us both sit down and play at the same table. Collusion? Hell no! We're both so competitive, we turn our monitors away from each other, and let 'er rip!
I talked her into playing a live tourney with me once...guess who knocked me out?????
After that...I just nod and smile as she goes off to play her slot machines!