I'm in the same boat as you. I couldn't deposit anywhere, but had a friend get me money on Cake. After spending months on Cake, let me tell you, it sucks. I would not play there. There are barely any games and support sucks, supposedly it takes 3-5 months to withdraw, and min withdraw is $500.
The merge network is the most popular place for Americans, that includes Carbon, Lock, and Black Chip. They actually have 10k people online most of the time and they run tourneys and sngs regularly. Also, lots more cash games running.
I'd recommend Merge. I haven't tried the really small sites.