just get a high impedance if you are going to be using a proper headphone amp or other output with plenty of gain. intuitively i feel like higher impedance will generally mean better accuracy vs lower volume.
lower impedance more useful for situations like: listening with your phone. in that case, 250 ohms just barely does it for me.
i bought my dt770 pros so many years ago… and they are really great, especially for long sessions. i have to take @wrl’s comments with a grain of salt because these are much flatter than any consumer- or dj-oriented headphones i’ve used… and more accurate ones, (like the grado reference series) tend to favor an open-back design (because physics) - this is often not practical except for a very controlled acoustic environment.
the dt770s do not maximize listening pleasure. word is that the newer “Premium” series is a bit flatter and “tighter” in the bass, but the "Pro"s are already much less bass-heavy than the norm.
i have also heard that the physical design on the "pro"s provides a tighter clamp and better isolation than the "premium"s. i dunno.
a big bonus is that i have been able to order replacement components from Beyer with no hassle at all, when things like the plush pads wear out. such a refreshing design policy. apparently they will also sell me drivers, cables, etc…
(just thinking back to my sony MDRs, when i had to strip the weird micro-insulation using, like, aspirin and whatnot, just to replace the cable…)