No paying to play online, plenty of F2P games that don't blow, your ability to use the input of your choosing, cheaper games, mod support, ability for users to revive old communities (Tribes 2 is alive and kicking by using a custom authorization mechanism), graphical fidelity (Even $550 systems can do 1080P/60FPS at higher graphical fidelity than XB1/PS4), ability to upgrade and customize your system without being XBL banned (New HDD because 500GB is too small? Banhammer), not being locked into buying officially supported peripherals, true multitasking, more exclusives, friendlier for indie development, and a more mature community. Should I continue?
AMD drivers don't suck in Windows, but have a worse track record under Linux. So it's really both.