As far as US players go I would rank the offerings in this order. This goes for service, support, deposit and cashout options.
Merge - Carbon Poker, the flagship, has gone all out with deposit options, decent cashout speeds, a new and improved VIP program and a rep that frequents poker forums that is on top of things. The network is growing fast on a percentage basis. There are quite a few other skins as well although be careful, some are related to Futurebet.
Poker Stars - Still the strongest brand. Financially strong, decent security and support. Burdened by echeck issues. If they weren't having deposit/cashout issues they would easily be #1. They will get through this as they always do.
Full Tilt - Same quality as PS facing same cashout issues, support and security are not quite as good but #2 in game selection.
Bodog - Bodog has always been surprisingly small. Now they have some unique ideas about player values that have shifted their focus. It has hurt their player counts. Still the brand is strong and their financial strength is almost certainly strong as well. If you want good lower stake games and don't care about anything else then you should check them out.
Cake Network - Cake Poker, the flagship, has had some reputation issues lately such as a massive shakeup at the top. They have added some decent deposit options and cashout speeds are faster and they seem to be trying to improve. Their support is very good and the promos are decent although sometimes a bit out there.
Cereus - Absolute Poker and UB.com have had endless cheating scandals dating back years that have yet to be fully resolved to this day. They have given a black eye to the online poker world. Still people play there because somehow this site manages to have the best cashout speeds and deposit options of any site. The game quality is also good. You won't catch me there though.
The rest are just non factors. Everleaf doesn't have much US primetime action and lacks in US deposit options, True Poker is too small and WSEX has serious cashout issues.