Chess.com is by far the finest chess playing site in the online world. I have played online chess for close to 18 years, and in my experiences playing online, I have never, ever, came accross a playing site that came close to matching, let alone surpassing what chess.com has to offer.
A lot of playing site that I visited over the years has something unique to each one of them. But the only playing site that has it all is chess.com. It is by far the most complete chess site ever made. No wonder that it's called the number one playing site in the world today!