I started back in the early days of PartyPoker due to the PartyPoker Milions cruise ship promotion. It was small back then. They became big because they understood and applied great customer service while fielding an impressive set of player promotions.
I moved to PokerStars for a while, but when FullTiltPoker was launched, I checked it out during the WSOP, and decided to try it out. Easily the best graphics package out there. Today I play mainly at FullTiltPoker and PokerStars.

There is very interesting site at
Online Poker at Bugsy's Club | The Worlds Finest Online Poker Room - Home with good programs and fairly average players. Graphics and players are good. When I was last there it had LOT of freerolls, so it is ideal place to play.
Despite numerous emails, PartyPoker does not seem to want to give their site a modern, open look. PartyPoker vs FullTiltPker is sort of the online equivalent of Taj vs Borgata in Atlantic city or Sahara vs Venetian in Las Vegas ... they are stuck in a time warp.