I'm not so sure Poker.com is a very big site, I often had problems finding tables at limits that fit me. It IS however a very nice site, with a good software, great features, decent bonus (30% on a max $200 deposit = $60) that's fairly easy to clear.
The foremost thing that makes Poker.com stand out (and I've said this many times) is that their customer support beats any other site I've been in touch with. I've sent them 6 emails, and each of them have been responded to within five minutes - and not just a "thank you for sending an email, we'll get back to you", but an actual answer to my question. It's like they have a guy assigned to wait for me to send an email, heh.
Poker.com and PokerStars are my two favorites. I like Paradise too, but don't currently play there.