If your son is familiar with the Wii remote, go with that.
The beautiful thing about this game is that those game pieces can be used across platforms. If you buy the Wii version for your son and he saves his character info on the toy, he can take it to his friend's house and play with it on the friend's Wii/360/PS3. The disc format is the only difference between the versions. I must say, it's pretty genius.