I'm from the US and an avid daily player. Personally, I like Global Poker. I even think that they have the highest amount of traffic for us players from the US. Some may argue that ACR has more traffic because their tournaments have higher guarantees, but there are some major tournament structure differences between the two. ACR offers unlimited re-entry plus up to 5 hours of late registration, which can really pump up that guarantee. While Global will not let you re-enter a tournament after you've busted and late registration never last more than 2 hours, and generally it's just an hour or less even. That being said, they are both good options.
I play at every place available to us here in the US and there is only one place I would recommend staying away from and that is Eveygame Poker/
juicy stakes Poker. Global Poker, ACR, Bovada, and BOL are all solid options. Pokerbros is an alternative I play sometimes, I would recommend it if you can find a trustworthy agent in a decent club. I don't play it often as it is just android/
iphone compatible. I'm in one club and could get you in if you're interested.
One poker room to keep an eye on is Coin Poker. I don't know a lot about them, but they are growing pretty fast and they do accept american players. I've given them a try and can't say anything bad about them yet. They have tons of freerolls too if you want to try it out at no expense. Hope this helps and good luck at the tables.