Should I buy Rockband 2 or Rockband:the beatles for PS3?

Hi everyone,
I am planning to buy a music playing game like Rockband
(I have never owned or played Rockband like games in any consoles and not a huge fan of either of Rock or Beatles )
but I LOVE Music playing games
I have been looking around to find more information about these two games but none of the information helped me decide which one is better suited for me
can anyone tell me good and bad about these games and your preferences and why?
Thanks