I have the Logitech G600, although I never play MMOs, I use it for shooters and Teamspeak Keybinds, I really like the 3rd mouseclick they added, as I use my indexfinger for my left click and my middlefinger for my right click, normally with this grip, my pinky would drag, but because of that 3rd button, my ringfinger can rest on there and my pinky can go on the side of the mouse. You can use that 3rd mouseclick for anything, like push to talk on TS or a quick aim button (lowering your dpi when you hold it, don't recommend this as it renders your muscle memory useless) (I use mine for melee).
Then you have like a ton of buttons on the side, which are angled so you can find every button easily, without having to look at your mouse. It also has 2 extra buttons on the top, most people would use these for profile switching or DPI switching. I also find it quite handy for navigation in my browser, you can tilt the middle mouse button to either side, which allows me to go back pages (you can of course, also bind this function to the thumb buttons.)
The backlighting on the buttons is amazing, as it shows me which profile I am currently using, it has some cool lighting effects as well from pulsing 1 color to going through the whole color scheme.
If you don't want that many buttons, I have heard good things about Steelseries mice.