Rock Band single player vs Guitar Hero 3 single player

My basic question for you all is whether the single player of Rock Band is worth playing compared to single player Guitar Hero 3.

More in depth: I got the Guitar Hero 3 wireless controller bundle dealy for Christmas, and while I am enjoying it, the gameplay seems kinda stale (just not as exciting as GH1 or 2 were back in the day). Last week though, I played 2 player Rock Band (just with guitars) at my friends house and it seemed so much more awesome than Guitar Hero. Now I'm debating if it would be worth it to just buy Rock Band (without the instruments - so I would just have guitar and mic) or even trade in GH3 for Rock Band. Is Rock Band's single player in any way worse than GH3 (guitarwise)? I'm not hardcore at all, medium is enough of a challenge for me, so I don't care about difficulty. It just seems like the only complaint reviews have of Rock Band's single player is that its "just like Guitar Hero" and they don't go in depth. So is it worth it?