I've never cared for PokerStars, didn't really like FTP. 888 is meh for some games (LHE comes to mind). iPoker is decent and I play there. PartyPoker, despite the hubaloo about segregation, is still quite fishy (PLO cash/MTTs). Ongame still has merit for some games even after bwin left. Also microgaming isn't terrible for some games.
Without knowing what you want to play, it's hard to say... game(s) and stake(s)...