PS3 is better because if you want to play online for Xbox, which is one of the main reasons people buy the 360, you have to pay $50 a year, where PS3 is free. Some people say that you do not have to pay for Xbox live, but you do if you want to play Call of Duty 4 or Halo 3 online.
Also it depends what kind of games you like. If you like sports games and Call of Duty 4, get the PS3. If you like Halo and Guitar Hero/ Rock Band, get the 360.