Now I play mostly on pokerstars and only freerolls on partypoker.
Sometimes I also play MTTs on Titan Poker because I had a winning when participating at an "on invitation tournament" which refilled my very old account there.
But I definitely prefer POKERSTARS even if I registered there very recently.
I play 2, PS and 888. PS, only because of Cardschat, and 888 because of the great amount of freerolls and micro sngs/trnies.. and I seem to do better at 888 in general.
I play in three different places, this is due to the variety of freeroll tournaments they offer and the sit & go since it is the modality that I play the most
I play at PokerStars,party poker,888 Poker,Black Chip Poker,GG Poker.Benefits are that I can choose which one to play at because they are all good online poker rooms.