The Wii is a good choice, I think, not because of the difference in the controllers (which are great, btw) but because of the types of games. They are far more likely to be played time and time again and appeal to more people, if you go in for the ones that really take advantage of the control style. I still play Excite Truck, a year and a half after I bought it, and TW's Golf is always a favorite, for example.
It's nice to have a game system that everyone likes to play. Joystick and gamepad games just don't appeal to many people. If I'm playing Wii and some people come over, everyone will enjoy joining in. That's why I say it's good if you will have only one system. If you are a gaming nut, you probably have several, so Wii can just be one of the choices, but it definitely distinguishes itself from the rest.