If you don't mind claw grip and a shape that is quite flat, go for the FK1 and not the "FK" version.
The extra length goes a long way in terms of comfort. It's not a mouse you can palm grip naturally, so I would only recommend it for claw grips with quite of bit of room between your palm and the back of the mouse.
The use is simplified to just plugging in and playing for me, and it's nice I don't have to worry about driver updates or additional software bogging up my computer.
It's probably one of the few mice out there with no real "flaws" for its intended use (which is mainly FPS games, and I'm going to assume you're an FPS gamer since you seem to know the importance of a good sensor). Since the FK1 uses the same sensor as the Rival, I think you'd agree that the avago 3310 sensor it uses is dead solid, and in my own use, it's only being outperformed by G502's sensor, 3366.
But you should be aware of its build quality issues - although I haven't had a problem with mine but I've seen numerous posts complaining about scroll wheel problems.
Another choice you can't go wrong with is G400s if you're looking for a more comfortable mouse and don't mind a slightly less performing sensor.
I don't recommend G502 personally because I found it impossible to use with all those macro buttons that make gripping it near impossible for my hands. It's also heavy and the inconsistent shape was discomforting.
