They’re so close in sound signature and performance, that you should pick based on whether you want the short cable and leatherette pads, or the longer cable with the velour. I’m not the only one to say that. Heck, Beyerdynamic says that in their marketing materials.
Which DT 770 for which source?
DT 770 Pro is available with 32, 80 and 250 ohms transducers, these also differ in application: the 32 ohms DT 770 Pro…
The 32 ohm and 250 ohm versions use very similar voice coils. The biggest differences are the pads and the cable, not the sound quality.
The Mayflower is more than enough to power pretty much anything.
I can’t do much more for you at this point! It’s in your hands now. :)