This is a really subjective question.
You can pick just about any decent mouse from any known gaming company and you should have very minor differences in performance.
One mouse may work better for one person, and another may work better for another person.
It's really about the fit and feel of the mouse. What you like, someone else may hate, and vice versa .
There really is no "best" mouse.
I used to play TF2 ESEA Intermediate division a few years ago. I had the opportunity to scrim with pro teams, and players like B4nny, cyzer, tagg, plat. and the like. A few of them had ****ty computer setups back then, due to a lack of funds. The one thing that they all had was incredible skill. Shade in particular, one of the best medics in the world, had a lol ****ty setup when he started playing on the worlds best teams, and he still did just fine.
So go with what you like. What ever feels good to you. Palm grip or claw? Layout of buttons.... Things like that.
I've always used a Logitech MX518, a palm grip mouse. It's been replaced by the identical Logitech G400, and now the G400s I believe.
The G500/500s is the same mouse pretty much with a few upgrades and a slightly higher scroll wheel, as well as a slightly larger thumb rest.
Just keep in mind that even with a great mouse, monitor, GPU, sound card and headphones, you won't suddenly become a pro player. A true pro player will still smoke you (and me) even if he is using ****ty equipment. And so it goes....