I only have the BDP-1 here for actual experience. This is what I've heard about the three models over the years when used to feed DACs (particularly their matching Bryston BDA counterpart number).
BDP-1: AES preferred over coaxial and USB.
BDP-2: USB improves and people start using USB more on this. However, AES is still preferred. There was also the introduction of IAD.
BDP-3: USB is right there with AES. It becomes a toss up. I've typically read this on BDA-3 and BDP-3 combos. No idea if it'd hold up on BDA-2 and BDP-3 for example.
The only way to conclusively say anything about them would be to pair each BDP # (1, 2, 3) with all the BDA # (1, 2, 3) to see if/how much of the differences sonically are attributed to the BDA vs. BDP. I haven't read much data about isolating the BDA and BDP to see what's what.