Personally, I'd get Rockband for the PS3. Better graphics, I want a PS3, and I'm sort of boycotting Nintendo products right now. ^^; Also, I think Guitar Hero sucks total butt on the Wii for the reasons of AB and C, but that's what I prefer.
For your situation, buy it for the Wii. It's easy because you already have a Wii and you seem like a Wii person. Invest money into your Wii more than any other system of our generation if you plan to play a lot of games.
