Funny to see ppl comparing wiimote pad and mouse while the games are not the same. Oh sure, some games (like COD's) are released on several formats but in this case, they are always dumbed down to suit pad(or even wiimote).
Just consider this :
In pure mouse/keyboard FPS, enemies are coming from everywhere (around, above and sometimes from beneath you). They move very quickly and the damage localisation is quite precise. Simply because the mouse allow very fast and precise aiming.
In pure Pad or Wiimote games, ennemies are usully coming slowly (sometimes remaining still) from the front (cause doing à 180° just take time), are dispatched on 2 or 3 even levels of high and most of the time, there is some kind of aiming assistance (larger cross, bullets following the target, etc.).
To compare these interfaces, you would have to play with them on a same, demanding, FPS, like Serious Sam on Hard difficulty setting. And my guess is that you would do well with the mouse, do OK with a pad, and just cry with the wiimote, because it's not just about aiming, but also moving and jumping around while following a fast target.
