Started to go off topic on another thread and realized this comparison should be a new topic.
I went to a dark site for observing yesterday evening with a friend. Well, last night actually. We didn't meet there until 9 pm and it was after 10 pm local time before it got dark enough for deep sky observation. And then the next thing you know it is 12:30 AM (and you were telling yourself you would pack up at midnight and you have only looked at a tiny portion of what is on your observing list).
I spent part of my time doing side by side comparisons with the OB 15x70 Ultra and the APM 16x70 ED MS delving into my preference for the latter. We had a lovely three day waxing crescent moon, 9% illuminated, and I forgot to bring the 82XL eyepiece case (a rare thing for me to forget an essential) so the 7mm XW eyepieces were not available for what would have been a fabulous view -- still quite nice with the 14mms. (Plus, a total of 11 binoculars were along for the ride so there was no dearth of equipment available. ) Anyway, I compared views of the crescent moon and of star fields with both the Ultra and APM.
The game changer for me was the discovery that the APM does not perform well for uncorrected near-sighted vision -- in this regard, the Ultra has a decided advantage. I mean, optically the performance of the Ultra is better than the APM when the instruments are focused for my uncorrected vision (-5.50 sphere in both eyes). But the APM has ample eye relief for eyeglass wearers and star hopping is easier when you can actually see stars to point the binocular so observing with my glasses on has become my standard mode with the APM. Interestingly, the problem with uncorrected vision is specific to that instrument -- the APM 12x50 ED MS is fine both with and without glasses. It must be due to some characteristic of the 16x70 eyepiece design. When wearing glasses, in all categories -- CA correction, brightness, sharpness, edge performance, and eye relief -- the APM is slightly better. Most noticeably so with CA -- well controlled and not objectionable with the Ultra, but close to undetectable in the APM. It's biggest advantage. The cumulative effect of all the small differences outweighs the disadvantage of its slight eye position fussiness for me, making the APM my 16x70 binocular of choice.
The OB 15x70 Ultra is an excellent binocular with a lot to recommend it and at a bargain price. The APM just offers a bit more in the way of performance -- not enough to show more than the Ultra, but enough to make a more pleasing view in side by side comparisons. It's twice the money. If that is a concern, or if you are an eyeglass wearer and prefer to observe without glasses (at least part of the time), you will be happy with the Ultra. Otherwise, my recommendation is the APM.