I would say the best sifes for usa players would have to be acr or bcp. Americas Cardroom, or Black Chip Poker as well as 64 spades. they all have many freerolls and easy cashout options. as well as player to player transfers.
I am going to wait for ACR 2.0 before I attempt any real $ on the site. It should be implemented by the end of the month. I am not a big fan of the current software as I have to play with the sound off as the alert gets stuck on and keeps alerting when its not my turn.
ACR and Black Chip Poker are two sites dedicated to the US player base. They use Flash plug-ins, I believe. The software is not as good as Stars, but it's alright. Similar to how 888 software operated before the recent reforms late last year.
Other connections can be established via tools like VPN, but that depends on your local laws and is strictly your decision.
America's Cardroom now that they are starting to clean up their act would have to be number 1. Bovada is also great and has a super soft player pool for cash and tourneys and they have the fastest btc withdrawals from my experience. Bet online isn't bad just they don't offer as big as prize pools for tourneys and their cash game pool is small.
I'm not an American player, but I know many poker rooms. In my view, 2 options are possible, Americas Cardroom or Betonline / Sportsbetting. Try them both and decide for yourself.