Hache-
GreenDoberman has it right, check out pokerpulse, determine your priorites, try a few rooms and decide what works best for you. I've played at quite a few of the rooms and Party has almost all my action with a few sessions at Pokerstars every now and then.
In a poker room my priorities are: 1) game selection (number of games and type) 2) player competency and 3) software ease of use. Most reputable rooms rank similarly on deposit methods, payouts and such so those features are a non-factor for me.
Party is the industry's 800 lb. gorilla and with that comes positives (great game selection) and negatives (bad customer service). Fortunately, I've only needed customer service 2-3 times in the past year so it is almost a non factor for me.
BTW, re Bigbet, give them a try at a minimum to support the Rx.
I did not have a great experience there for a couple of reasons but a few others did enjoy playing there. The "splash pot" is overrated as it is chosen by the pokerroom manager and it just so happens that when there was an Rx "outing" there we were splashed 2x in less than 5 minutes. Most people would be happy about that but I saw it as bias on the part of the manager. What if you were at a different table that was not splashed but you obviously contribute to the rake just as much (if not more) than we at the Rx table did? (To BigBet's defense they never advertised that this was random.) Anyway..give them a try but I don't think I'm their target customer and they have little that appeals to me.
Frankly, similar to the sportsbook industry there are TOO many pokerrooms for all of them to survive. In order for a room to take a chunk of customers away from Party/Pokerstars/Paradise, it will have to offer something other than a generic online poker experience.