H3 sucks in my opinion, h2 is better. Guitar Hero all the way. I'm not the best but I love it. I try not to get too crazy w/my friends, but when I'm alone... You don't wanna know!
Well, 2 whole different kinds of games at which neither have really much if anything in common. It really depends on what type of games you like to see which you like better.
halo 3 is better for me although some first person shooter games make me dizzy and i feel like i am going to faint but that usually happens to fps's that have bad graphics which halo 3 has awesome graphics.
Halo 3 much funner, Multiplayer all around the world, and guitar hero has hard controls with the guitar and all you do is hit colorful buttons and you can play similar games like Guitar Hero 3 online... But Rockband is awesome!