Ah, when I read the title I was wondering why you didn't add a poll, your explanation makes sense.
Anyway, since you care so much about our opinions...
For an fps game, how well you do depends on how accurately and quickly you can take someone down. The keyboard is just for movements and nearly ANY keyboard will be just fine for that job. So the mouse is gonna give you a much more competitive edge than a keyboard would because the accuracy is allot more dependent on what mouse you have than what keyboard you have, trust me, I have experienced it myself when I bought a new mouse.
Other than that, mmorpgs depend more on keyboards for accuracy as your attacks are mapped to the keyboard buttons and are accessed more quickly by using the keyboard's hot keys than clicking on the icons on-screen with the mouse. This also applies to some strategy games. And lets not forget the macros, macros are very important to these gamers so a keyboard has to have them.
So it depends on what games you play that will determine which is more important, to me the mouse will be more important as I play first person shooters more competitively than I do other games at lan parties.
