The reverso is certainly the signature JLC imo, but the MC series is beautiful too. I always find myself asking the same question--did I make the right choice? If I had one JLC it probably should have been a reverso, but at the same time, nothing ever spoke to me as much as that dang MUTM so I am happy. The 1931 in black is never far from my thoughts. If it had an open caseback I dunno what I woulda done. Sometimes they make your decision easier.
I've always fancied the Reverso since it is a true icon in the world of watches. The MC series is a fantastic line of watches. My only reason for leaning more toward the Reverso is my Dad has a MC 8 Day Reserve that I might inherit some day.
I can tell you I was traveling a few months ago and I got to try on the 1931 with black dial...its stunning. I think an open back would be killer on that watch, but I understand in keeping with originality of purpose and design that they used a solid back.