I used to play with the Gamecube Controller (and I still prefer it,) but as of late I seem to be used the Wiimote held sideways, mostly for the sheer convenience of picking up my remote, turning on my system, and playing, only needing to pick up a single device to do it all. Plus not having to deal with any wires.
It also makes me not play quite as good, which I like since I generally kick a lot of hindquarters. It makes fighting a bit more challenging.