The DT-770 Pro 80-Ohm has the most bass, the DT-770 "Premium" 32-Ohm has the least bass (but still good)
I would "guess" the IPod can decently power the 80-Ohm.
The Premiums have a lighter clamping force compared to the Pros.
If you like full bass, get the Pro 80-Ohm and with the money you save over the Premium 32-Ohm, buy a portable headphone amplifier.
It might change from phone to phone.
Apple store recommends AKG702 (78-ohm or close to it, but it was below 80 ohm for sure) and say it sounds good our of IPod. I'm yet to come across people that support that statement.
Probably someone with iPad + DT770 80 ohm can feedback.