Jeez its simple...
Analogue movement is marginally better than keyboard (if you use W = forward and left/right are strafe and you steer with mouse). And that difference will make almost no difference in any FPS (which is going to be combat orientated).
The main point is the movement advantage is small and makes no difference to gameplay that I've ever noticed.
Mouse aiming is much more accurate that analogue stick. And it makes a huge difference to gameplay and allows for more open level design - FPS design for console always tries to minimize extreme use of Z vertical, keeping you mainly in a level combat environment or slight height differences. With a mouse FPS can have extreme Z combat.
The main point is aiming with a mouse is a big advantage over analgue.
Therefore overall for FPS K&M is better as what you gain is much more than what you lose and is more integral to the gameplay of an FPS as well.
As for Wii mote and nunchuck are you kidding me? For FPS it slightly edges dual analogue but the aiming is way below mouse yet again - probably better for your wrist muscles though if you want to play a long session of very fast paced online MP FPS...
Try to be reasonable... its easier than you think...
