I've owned both but ultimately decided on the G502 which imo is the superior mouse.
Logitech G502
Pros: Fast, Responsive switches
Optical Sensor
Weight adjustable
Customizable led
Comfortable grip materials
Excellent button placement, very easy to reach
High dpi 12000 max (iirc)
Cons: a bit on the small side, comfortable for claw grip however, but, if you have large hands or use palm grip it may be a bit awkward.
I'm kinda biased towards this mouse so I admit don't have any faults with it whatsoever.
Corsair M95
Pros: Tons of buttons
Good build quality, very sturdy
Clicks are very responsive but a bit too sensitive imo
Cons: Heavy, no weight adjustment (My main gripe)
Buttons are in a strange config and take awhile to get used to (which I never did). One or two were so out of place I never bothered to use them
Mouse material is a smooth glossy finish which was not comfortable to grip and became slippery after long sessions when sweat built up
Hope this helps