The 8BitDo Ultimate controller 2.4ghz version is the best for the steam deck. They released a cheaper version if you don’t need/want the dock. RetroGameCorps has a video comparing all the different versions of this controller since it is a bit confusing.

If you prefer 2D games and primarily use the d-pad then the 8BitDo Pro2 controller is best for this. Note this is only a Bluetooth controller and for fast pace games you will notice some input lag on the steamdeck. I bought a 15ft usb cable to just plug it in and play on the couch. I haven’t tried 8BitDo’s wireless dingle with it to know if this removes the input lag. I might try that this evening to find out.

This, I had been a sync user for the past decade. Will immediately install sync for lemmy when it releases. Likely the pro/ultimate as well once available.