It depends, do you enjoy playing instruments with your friends and is the extra cash for RB not a big concern? Then get rockband.
If you are mostly interested in the guitar portions of songs, don't really want to spend about double the money, and enjoyed the other GH games then get GH3.
Personally my choice is made for me: Owning only a Wii for current generation systems means no RB available. With that said it doesn't appeal to me much anyways since I am in this type of game for the crazy guitar solos and insane face melters. Plus I love Slash and am really looking forward to the song he wrote for GH3.








