While one of the best things about having a gaming-spec PC is the sheer freedom you have in input devices, it really does help to have a reliable, widely supported gamepad. My current go-to is the XBox One controller, but there might be another competitor on the horizon. You'll have to opt in to the latest Steam beta to use it, but you can now use a Nintendo Switch Pro controller on Steam, remarkably useful gyro-aiming and all.
Oi, you, stop laughing at the back. Anyone who has played Splatoon to any pseudo-competitive degree will be able to tell you that gyro aiming is what makes that game sing - see the video below for proof. Your analogue stick handles the broad strokes in aiming, but properly configured you can line up a precision shot by just tilting the controller a tiny bit. It's not only effective, but remarkably satisfying, and rewards steady hands in a way other devices don't. Plus, it's far more intuitive for people who tend to go heavy on analogue aiming and find themselves overshooting targets.
On the whole, the Switch Pro controller is largely similar to the Xbox One design, only with a couple extra function buttons on the face, a slightly different D-pad design, plus the perk of gyro aiming. It also has smoother, more granular vibration support, although most PC games wouldn't know what to do with that. Hopefully some indie devs will lead the charge and start natively supporting it, but at least regular XInput vibration should map nicely to it for now.
As this is all integrated into the Steam Input UI, you can not only use official controller profiles from Valve, but create your own and share them with others on a per-game basis. It'll be interesting to see what people come up with. The Switch version of Doom 2016 already has some pretty well-tuned gyro-aiming, so it'd be nice to see people use that as a base template for FPS's. Plus, this should provide an interesting new mid-point between traditional gamepads and the Steam controller's touchpads.
For those considering jumping on the bandwagon without even owning a Nintendo Switch, be warned: The Switch Pro controller costs a pretty penny, coming in at around £55 RRP in the UK, and $70 in the US, making it one of the more expensive controllers out there, but it does at least have the advantage of Nintendo build quality.