I've been using this Logitech MX Master Mouse for a few days now and I can definitively say that it is the best mouse I have ever used. It is ergonomically shaped to the resting posture of the hand and it includes buttons and actions for just about anything you want (everything is customizable). The mouse comes in 3 colors and I opted for the "Stone" color you see above (it just seems to fit a little better with my mostly dark setup). Anyway, this is Logitech's top-of-the-line desktop mouse and it amazingly can track on glass (something I think the MX series of mice have been able to do for a few generations now). But to me, this seems revolutionary because I've never had a mouse that could do that (I have a much older version of the MX Mouse -- maybe the first release of it -- that could not track on glass).
If you want a new mouse, I would wait and see if this goes on sale again. I would have never bought this for retail price, but for that amazing half-off sale price, I had to make the leap. I'm glad I did.