Also something to consider if you go back and play a lot of older games/emulated games, a secondary controller like a logitech gamepad with its physical x/d input switch is nice to have.
I've used just about every PC gamepad option there is and the only controllers that are bearable at all to me are the PS1 classic controller, the SNES mini or SNES wii controller with raphnet adapter, the Retro-bit Sega Genesis licensed USB controller, and the Hori Fighting Commander. Out of those options I would recommend the PS1 classic controller above them all. It has a much better dpad than the PS4 controller and you can get brand new ones on Ebay for $20 vs spending way more to get a new Club Nintendo SNES Wii controller for $50 + $30 raphnet adapter.
The Raphnet adapter is supposed to be very low latency, but the PS1 controller still feels more direct to me as well. As for the Retro-Bit officially licensed Sega Genesis and Sega Saturn USB controllers, I bought both and the build quality of the Genesis controller is much better. The Saturn one has very loose buttons that rattle around and tolerances for the dpad are also bad where it hits up against the shell a bit when I press down making it kinda annoying to use.
Having said that, even though the Genesis build quality is better, it's still not as good as the PS1 classic controller. For the Hori Fighting Commander, the dpad is decent, but it's kind of a big and bulky controller compared to everything else which tries to force your hands into always having your pointer fingers on the L+R buttons, which I HATE controllers that do that, especially on a 'tretro' controller that has no business doing so pretending it's an FPS controller.
