I'm a gamer so mouse lag, battery faffing and so on is not acceptable. I use the wireless G7 from Logitech and I can vouch for it's sensitivity (it cried like a trooper in my last TF2 session). It has many levels of sensitivity and is a good solid mouse.
Before that I used a refurbished MX700 (?) that I got with a wireless Logitech keyboard through EBay (important as the cables are never long enough to reach my tower). I was genuinely gobsmacked at how good it was and that combo served me well.
Unfortunately it used rechargeable AA batteries and the cradle (which you were meant to slot your mouse in and charge up when not in use) was broke for me... so I had to use a separate charger and it got to be a pain in the end (not to mention hearing horror stories of batteries being charged exploding into flames

).
So where the G7 is even better from my perspective is that it comes with two little battery packs and it's own (working) charger. You just slot them in, use them up, and then switch between as you go. It's very simple, fast and efficient.
If you want wireless the G7 comes highly recommended. Don't believe the myth that they don't compete with wired. I've had wireless and wired plugged in at the same time with no difference and for ergonomics and just downright ease of use - the wireless wins every time.
If you can get a working MX700 on the cheap I'd recommend that wholeheartedly - it's a very good mouse (although there are even better variants before you get to the G7)