all three are good in different situations
mouse+keys are good in games that require aiming (FPS, some TPS)
controllers are good on fixed cameras (other TPS , fighting games , racing games)
motion sensors are mainly just good for gimmicky games like the wii sports games and rayman raving rabbids and rail shooters such as the house of the dead games. all though red steel was the one good serious wii game i have played and i think i know why. the makers of red steel didnt use gimmicks the used the motion sensors practically (i.e they didnt make you try to throw a grenade by imitating a throw they just gave you a grenade button and also they only used simple motions like a quick downward flick of the nunchuck to pick up a weapon)