Really depends on where your from. If your from the U.S. then your best bet would be The American Cardroom. It's not that their really better than the other sites in terms of software, but from what i've seen, there is just more action on ACR. If there's one thing i want from a site, it simply is action and being able to instantly find on-going ring games and a good selection of tournaments that would not be cancelled because there was not enough registered players. Looks like ACR has the most players right now. More players=more action.