I too have Momentums, P500s and P7s. Frankly they can all sound reasonably good out of an iPhone 5S but significantly better out of a boosting amp. The comparison with the the PSB M4U2 is instructive here with its built in amp providing more realistic depth and scale straight from the iPhone. Given that the sound from all three is acceptable , differences in comfort and portability become more significant. For me the Momentums are most comfortable being light and sufficiently ear-enveloping whereas the P500s are too light and never seem to seat comfortably. Significantly, the KEFs sound far better when pressed against the ears, always a sign that normal seating is unsatisfactory. The P7s are reasonably comfortable but feel relatively heavy and unwieldy to me. Here their substantial luxury build is a disadvantage. While they may not be significantly heavier, they feel it and they are certainly more bulky. So the Momentums come out top on the comfort and seating stakes but their portability is severely compromised by their absurdly bulky carrying case. This case is great for storing them at home but takes up far too much room in hand luggage. The phones themselves don't fold neither do their ear cups flatten which are disadvantages compared with the P7s and the P500s but they are much more portable in a soft sac. I use the luxury pouch from my Ultrasone Edition 8s, a phone I can't get on with due to a piercing mid, but thats another story. Thus accommodated the Momentums are more portable and I am sure there are many third party alternatives to the Ultrasone pouch. Sennheisers do provide such a pouch with the smaller Momentums and I would advise them to provide something similar for the larger 'phones.
Returning to the sound of the phones and that elusive realism we all seek I have to identify some reservations with the P7s. Although everything is there and the frequency bands are well balanced there is some element standing between me and the desired listening experience.I can only describe this as a very slight coloration in the mid band which gives music a slightly honky metallic sound when immediately compared with other phones. I don't have this problem with either the Momentums or the KEFs. They are different from each other in that the Momentum has some mild bass emphasis and warmth whereas the KEF is more open and transparent. However the best KEF sound requires additional pressure on the cups which is not practicable.
So my conclusion is that the Momentums are the best all rounder provided they can be accommodated in an alternative soft case. Come on Sennheiser, listen to criticism and give the larger Momentums the same facility as the smaller.
This is intended as a three way comparison but I have to add that I often find the Sony MDR 1R at least as good as the Momentums but with a better sense of depth and space. They fold into a convenient soft case and are very comfortable. Many critics claim the Sonys lack ultimate detail but so do the Momentums and their softer presentations are , to my ears, far preferable to the ear splitting detail of, for example, Grados. Maybe my reservations with the P7s are in the same area.