You can click on Poker Site Reviews on the Cardschat website to get their recommendations. My three favorites as a US player are America's Cardroom, Bet Online, and Ignition poker. Try out all three and pick out which you like best.
PokerStars has really shitty rakeback but it's great in general, good software and many kind of tournaments with more players bigger guaranteed prizes etc.. I know that Natural8 is becoming really popular now. Second best site after PokerStars is partypoker for sure. I recommend you these 3 sites what I mentioned.
Pokerstars has the best prize pools for it's tournaments , also a variety of games offered and the best client programm in the card room market , but tougher players to play agaist . Ofcourse you can play at PartyPoker or 888poker , they have great offers and promotions , satellites and games to play and also imo easier players to play against (at least at the micros) . gl