Which one is better?

As is my understanding at the current moment..

Pro III is lighter, and more expensive, and stronger.

But are they as reliable?

pro 3 has larger bearings,and future proofed so you can convert easy to 15mm or 20mm axle plus a more robust freewheel

Are larger bearings better? (sorry, but my technical knowledge only goes so far..)

And pro3s arent non disc/road hubs are they? Can you get a disc version of a pro3?

My understanding was that there’s a road/non disc pro 3 and a disc/off road pro III. I think the pro III might only be available as a built wheel using the straight pull spokes. It also has the option of a 3 or 4 bolt rotor setup.

I don’t know if the bearings or freehub are different but bigger bearings are not always better where as bigger balls inside the bearing generally are.

You can convert pro11s between 15mm and 20mm pretty easy already.

The bearings in the pro3 are custom they only come from hope as far as i know so cost you 3 times as much.