Where should I play for BONUS and quality of play?

[Sandwich]

I already have accounts on Party Poker and Pokerstars... never done the bonus thing and I feel like I'm missing out on some "free" money....

If I had, say, $600 or so to deposit into an online poker site, where should I play to get the best BONUS and best play?

I liked playing on Pokerstars but lost all my dough there... do they have a re-buy bonus that's any good?

Thanks for whatever advice you have.