I started on
Full Tilt, and I still play there, but my bankroll for that site is waaaay low, but I get rakeback there, so I try to play there as much as possible.
Next I went to
Bodog b/c I got an instant 10% bonus for signing up, but I have also ran my bankroll too low to even play a sng.
Then
Pokerstars, but again, bankroll issues. Too many bad beats at that site.
Titan is just awesome. I love the short-handed limit games. I've been killing it there. Plus the BBP tourneys are sweet!
I also play at PokerWorld.com, b/c I get awesome rakeback.