Yeah the DT-880 and HD-598 are not comparable at all. It all depends on preferences. I loved the DT-880 for awhile when I had it but needed to get rid of it due to comfort.
I found it to actually be very neutral and completely uncolored when properly unamped. It didn't try to make any of my music better than it really is. Want a headphone to make your collection sound like garbage? Get the DT-880! Don't take that the wrong way because its just that it's very revealing and detailed.
I found the mids to not be too recessed, but they are perhaps very, very slightly. It was such a non-issue for me. It took me awhile to notice this and I didnt until I tried them with games and everything was so distant compared to other neutral headphones.
The DT-880 is kind of boring and lifeless with some music and then really fun with others. It was quite confusing. I loved mine for electronic music. In the end I decided to switch to the K702. To my ears, the K702 has far more treble.
The HD-598 has better mids than the DT-880 and they're far more forward, but the DT-880 is less forgiving of source files and is much more clear and revealing. The soundstage of the 598 is massive compared to the DT-880.
I've owned all 3 DT-880's and I won't go into the differences. I prefer the 32 ohm version.
The HD-598 to me is definitely more fun to listen to, but it depends on what you listen to. It does make music a bit more fun to listen to and colors it a tad, but who cares? I don't!
Not sure if you plan on playing games or watch movies with them, but if you do, get the 598. I found the DT-880 terrible for movies and I never liked it for gaming. It's decent for competitive gaming though.