Which one should I get?

that's my go to controller, it's pretty great, only thing it sucks at is fighting games but anyone that's serious about those uses a fighting stick anyways

Got it for 25. Turns out it was the last one at the store.

Why didn't you tell me the D-pad was a flimsy piece of shit?

So what's the consensus?

My brother bought it and I don't know what to test it out on.

Had mine for little over a year. It is my primary controller no doubt. Took some getting used to but using regular controllers feels pretty awful now. It obviously isn't going to replace your mouse for fps games, regardless of what Valve thinks when they push CSGO with it. But I've been loving it in Dragon's Dogma. It is perfect for aiming bows and shit and is still great for the regular button mashing attacks. Granted the buttons could be a bit bigger.

It's okay. Especially for 25 bucks, you get a controller that lasts for a while. What it needs, though, is separate drivers to use it without Steam.

Haven't messed with the steam controller outside of steam beyond using it as a wireless mouse when I'm sitting on the couch. Worst case scenario you can just add games as non-steam and get all functionality.
I doubt Valve will release separate drivers because A, they want to keep it locked to their platform and B, it would require somebody at valve actually working.

So, which controller has the best d-pad? Also,

To play MIDI music, obviously

you have to use foss/open source drivers written by other people
like github.com/ynsta/steamcontroller for example

Why isn't that a standard? Sega got it right with the Megadrive.