Pokerstars is the first choice for many advanced poker players, perhaps due to Poker tars' excellent software and its wide variety of tournaments.
Pokerstars has earned the reputation of being the industry leader when it comes to online tournaments. The site is second only to Partypoker when it comes to tournament traffic. You will see tournaments with up to 1,500 players, without it causing any problems for the software. Pokerstars also allows players to upload their own pictures at the tables.
Pokerstars also sees plenty of ring game traffic, with up to 4,000 players during peak hours. Note that Poker Stars started the trend with micro-limit games. The limits go as low as $0.01/$0.02. There is no rake on these games.
The competition at Pokerstars is very tough as the site attracts plenty of advanced poker players. It's not uncommon to see view the flop percentages in the mid 20s and low 30s.