888poker software is quite stable. Well, Pokerstars is incredible because of so many years of improvement, but I never had any problems with 888.
It is good to remember that 888 is still one of the few sites that offer great variety of tournaments at small price, such as $0.10 (full ring one table sit and go, and even 3 daily tournaments with $25/$30 gtd).
PokerStars is absolutely amazing, but for instance, it just offers a 18-45 players SnG at $0.25 or $0.50, and for MTTs, I just know the daily The Hot $0.55.
Also, 888 may be the room with more freerolls available for those who are starting.