My Logitech has a clicky wheel, but not nearly stiff enough to prevent inadvertent scrolling when clicking it. I mean, you can do it without that much issue if you're careful, but in what FPS do you have time to sit and carefully click a button? I've had this mouse twice over, and neither time did I consider that button usable for anything that required timing. Occasionally I'll have it set for something that I use outside of combat or whatever, though.
I can't even remember the model of mouse I have. I really like it, though. It's probably like a 2nd or 3rd generation wired optical mouse, so it's pretty freaking old, but it just never dies.