For "General Purpose" without any extra drivers or stuff... The "Standards" for PC controllers are...
* Gold: XBox 360 -- Wired (~$30) or Wireless (~$40-45, packing MUST state "For Windows" as it includes the USB Receiver) that works for pretty much all Windows PC's with minimal issues. You can connect up to 4 controllers to the USB wireless receiver, so you can easily get more controllers elsewhere.
* Silver: XBox One -- Bit more expensive (as the Wireless USB receiver is $25), but has similar layout as the XBox 360 controller. HOWEVER, this is restricted to Windows 10 officially (Microsoft refuses to provide drivers for older versions of Windows). Receiver still supports up to 4 controllers
* Bronze: Steam Controller ($50) -- While geared to work within Steam, it's pretty flexible for all PC games... including those that don't natively support controllers. You may need to add non-Steam games / emulators into your Steam library, but it's a minor deal.
You can use Wiimotes & PS3 / PS4 controllers, but you will need to have a BlueTooth connection (either built-in to your computer or via a USB dongle) in addition to software to convert controller input into PC-understood stuff.
For emulators, you can find retro USB controllers (Atari 2600, NES, SNES, GEN, N64 & Gamecube) for $15-20 / ea. if you want to stick with the original controls... but that's more personal preference.
Hope this helps!