Re: It's whatever you're used to.
Mouse is generally better suited for anything involving looking and aiming. For those things it is genuinely better than thumbsticks, simply because of the response time involved in executing an action. Turning around can take several seconds, and fine aiming longer. With a mouse I can do it in a fraction of the time. (I play frequently on both kinds of controller.)
I wouldn't like to say that the console controllers are inherently less accurate, as I'm sure some people are daemons at aiming with them. For me, they are. I can aim to a much finer degree with a mouse, in much less time, with much smaller adjustments possible, and I find myself often cursing on console FPS games along the lines of "I wish I had a bloody mouse for this bit".
Plus, I can adjust the speed/resolution of my mouse via a couple of hardware buttons, letting me switch instantly between aiming types. That's useful in games like Killing Floor when I'm moving between my primary murder machine (say, a SCAR) and my secondary run-and-gun weapon (say, a shotgun). I can aim insanely accurately when the muties are at range, and when they get a bit cuddly I can switch weapons, jack the res and run for it.
Not that I game much. *Cough*