I normally use my razer death adder 2013. I also have a razer black widow mechanical kb from around that time too. Now the thing is, I thought I would be more efficient getting a new mouse, so I got a logitech g600 recently. It's an awesome mouse and it does make some things easier. However for me it is also highly dependant on what class I am using, as I find myself going back to my death adder quite frequently. To be honest, it has enough buttons but I do also like my g600. I wvw primarily so I actually have both mouse side by side but atm I disconnected g600 to make more room on my desk. I have all classes and I am a build whore, I have some kind of addiction to it and all weaponsets so having these two mouse is nice. I find myself using death adder on engi/mesmer/thief/ele/ranger/guardian/warr/rev...actually all of them. The g600 is maybe useful for my engi & ele rotations as those two classes are a little similar in the way they swap toolkits/attunements, and I see this probably very useful in stuff like raids maybe, but it definitely works nicely in wvw. If you have a friend that has a mouse with a lot of buttons, ask if you can borrow it for 1-2 weeks and try, then you'll be able to come to a conclusion if you feel comfortable with it.
Update: egads. Just reread your post lels. Ok, when I was buying my g600 I read there was another alternative which was the corsair scimitar but at the time I did not know where to get it, maybe that could be a more comfy on the hands option.
What is the best MMO mouse?, what do you use?