On Wii, Rock Band is trash. Not sure about part 2 but the first one was the laziest port I've ever seen of a game (no online play, no downloadable content, hardware breaks easily). I was very disappointed with it.
Guitar Hero World Tour on the other hand is excellent, not a bastard child version compared to the Xbox360/PS3 versions (actually has stuff they don't have like Mii Free Play mode) and the drum set is awesome. Plus it has downloadable content to get new songs
