You can play Gamecube games on the Wii, that's a plus. Also the price tag. Unfortunantly, it's still hard to find one.
You can go either way with a 360 or PS3...of course the Blu-Ray is PS3's biggest selling point, especially with HD-DVD going bye bye. So far there are no known issues with the PS3 whereas the 360 has the ol red ring of death thing going on. I have a 360, and I do love it, but I'd probably go with a PS3 if I were you. Get the Wii as well if you have the extra cash.
I haven't played the latest WWE game, but I hear it's garbage, no matter what system.
There are versions of Guitar Hero on all 3 systems, so it doesn't matter there.