Best is relative to what you need. How many programmable buttons do you need? Do you like simple, or as many frills as possible? Do you care about aesthetics?
I'd suggest a Logitech G502 Proteus Spectrum if you are looking for an FPS mouse. I grabbed it on sale at Best Buy for $50, and is still on sale right here on Amazon if online shopping is your thing. You can make it light or heavy with the weights (I put all of them in since the added heft makes it feel more premium), has 2 modes for the scroll wheel (free scroll or notches), and has 6 extra buttons to map. And of course, full RGB lighting for that true gamer aesthetic.