I have both cans and they are great cans. you can't go wrong with any of those.
overall, I can say momentum has better sound. Bass is firm and tight, high is more crisp and mid is silk smooth. The balance is fantastic and the resolution is amazing. It has audiophile quality sound.
mdr 1r is almost good as momentum, but it sounds bit veiled compared to momentum. bass is slightly loose and high is little recessed. but mid is quite good and rich, and soundstage is surprisingly good. (better than momentum)
I think mdr 1r is the most comfortable portable headphone. period.
mdr 1r is very good looking design, but momentum is really really beautiful, elegant and unique design that stands out among headphones.
even though mdr 1r is mostly plastic (housing is metal, aluminum), bq is very good.
momentum is top notch, stainless frame, hight quality leather ear cups and headband, very unique adjustable angled connector..
momentum is superior in lots of way to mdr 1r, but I am listening mdr 1r more and more. momentum has definitely better sounding headphone but mdr 1r is more appealing to me. it has warm, rich sound with good soundstage and less fatigue sound signature, and very comfortable so you can wear it for a long time. well, i love both cans, but I would go for mdr 1r if I have to choose one.