Buy the cheapest one you can find, have an SD card ready, grab the first youtube movie about softmodding and 30 min later your done.
Mostly because the Wii doesn't have any sort of reasonable security system. It was exploited to death very quickly.
Well the fact that they did not improve one bit the security measures on the GameCube side of the console opened the doors of the Wii system right away. With a foot in the door, it was just a matter of time before someone would break the barrier between running in GC mode and running code in Wii mode.