Moment skis are sick, and you can't go wrong either way. It just all depends on WHERE and HOW you ski...These are both pretty fat, powder specific skis, but they both will ski groomers decently if they have to. For their sizes, they actually do well on hardpack, but not as well as thinner skis...obviously.
The Bibby Pros are going to be a more versatile ski, as they're a bit thinner and stiffer. They handle hardpack much better than the Night Train, due to the added camber underfoot. The Bibby is not going to give up too much pop and play, but they are less playful then the Night Train. The bibby is a hard charging ski, that you can still Jib around on without any problems. Bibby Pro would make a better all mountain ski.
The night train is flat underfoot, so it's similar to a full reverse camber ski (full rocker). There is no camber underfoot, and its specifically designed for soft snow booter sessions. It's definitely what you call a jib ski, and it's going be the best ski for you if you intend to be spinning of backcountry booters and/or surfing deep, fresh snow. They're less grippy than the Bibby and wouldn't make as well of an all mountain ski.
I cannot tell you which ski is truly better for moguls, but I would go with the Bibby Pro is you intend to be using the skis for a variety of conditions and terrain.
If you're not going to be skiing a lot of powder, you may want to check out the Moment PB&J. It's basically a thinner Bibby Pro, built for all mountain, and can handle a variety of conditions better than Either the Bibby or Night Train.
Ski Yellowstone. Jackson Hole. Grand Targhee. Big Sky. Bridger Bowl.