what is the best mouse sensitivity?

Answer 1

You want it to be fast enough that you can easily move around and not lose the mouse cursor. I also believe that your screen resolution can impact this as well. For bigger screens, I usually move the sensitivity up so I can move from one side to the other fairly quickly.

Answer 2

just fast enough to reach all ends of the screen while moving only your fingers while resting your palm on the mouse pad, but not so fast you lose fluidity of movement