One that fits ur hand. Same with mice. They are all the same. Headset and monitor are the only accessories that can give you an advantage
its not that important compared to headset, mouse and pad but once you get to the mech keyboards you never go back to normal one
I dont think they matter at all, having mechanical for better feeling obv, I have some low budget 50bucks brown switches and its great, its some noname brand, but since I have mechanical I like to type a lot more.
Just find some you like, maybe rgb, switches, I also prefer shortened version of keyboards, they are best
Doesnt matter not even 50% as much as mouse or headset