I've come to realize that KB is still THE BEST lately. Even as old as Doom, there's enough verticality to make KB worthwhile, and the weird perspective you get from looking up or down too sharply at tight spaces can be avoided by, well, not doing it, since doing so is never necessary. Strafing and 180 turn is easier, so the difficulty doesn't come out of frustrating control scheme. Your reflex is too good for the game to be challenging at normal difficulty? Turn it up!