Guitar Hero is more fun to me if I'm alone or with one friend, but if you've got a big room of people, Rock Band seems way more fun. But overall, I'll def go for GH
Guitar Hero is probably best for solo players, especially the guitar on the earlier games. When drums and vocals were released, they weren't very good so Guitar Hero: World Tour was probably the worst game of the series. After that, they got a lot better, but still not great as a band
Rock Band is better with a group of people playing as a band. It isn't much different from the Guitar Hero band setup, but somehow it is much more fun to play. Rock Band 2 is a lot better for solo players, but Guitar Hero is still much better.
I prefer Guitar Hero in general, but my favourite game is probably Rock Band 2
I prefer Rock Band over Guitar Hero. Rock Band has the widest variety in songs. Rock Band is still good for solo play, even if it does have 'band' in its name.