Personally I like the momentums a lot more than the beyers.
Sound Quality: Going off a bit of memory here as I no longer own either, but the Beyers had a pretty decent V to their sound sig while the sens are a bit more neutral/ mid prominant. They also ran a little hot in the treble on certain tracks with some occasional sibilance, whereas the momentum seemed a bit warmer and forgiving. The DT1350 does probably have a bit more clarity and extension in the highs though. As I said mids somewhat recessed on the beyer and a little more analytical, the senns being a bit more forward and warm/engaging (reminded me a bit of the HD600 or Hd650). Bass of the DT1350 were a little more weighty and better extension than the momentums.
Build: DT1350 feels like a very well made phone in the hands with a great little case that it fits into. Really built like a tank. Momentums come off a little cheaper feeling, mostly because they don't have that solid metal/hefty feel. I'm sure they hold up fine over the long haul though.
Comfort: DT1350- not very comfortable for me, pads sit a little more centrally on the ear which can cause some discomfort. For me it was hard to go over an hour before they became noticeable. Momentum- fairly comfortable and if I remember correct a bit lighter overall.
Portability: I'd say beyer. Comes with a very sweet little case that is very convenient to pack around, they also sit around the neck a bit more comfortably. Momentum case is a little more bulky, but probably a lighter package overall if I remember right.
Like I said though this is all going off memory.