I play at Pokerstars and Party Poker. PP has the free bonus on your first deposit. I am friends with a top 50 finisher of the WSOP this last year. He's rated as a top internet player now. He's on Paradise, Ultimate Bet, and a little of PP and PS. To be honest, he had his account on Paradise hacked about 3 or 4 weeks ago. He's well known, so he was probably targeted b/c of that. Turns out they took $25K out of his account. A week later, Paradise was close but still hadn't found out who did it. They still credited his account with the full amount. I would say those 4 (and probably more) are trustworthy. With the money they make there, there is no reason to fix it and I've never heard of any big time collusion. I haven't seen Paradise in action but I've watched UltimateBet before. Seemed like it was a bit more serious at UB and more by the book. Fewer showdowns and lots won with raising action.
I mainly play little $5 sit and go's nowdays. I like tournament style. On occasion I'll sit at the quarter tables and play ring games or try a cheap multi-table action.
I have several friends that play PP, PS, UB everyday.