Celestron SkyMaster Giant 15x70 Binoculars vs Nikon Action 16x50 Binocular?

These 2 binoculars has similar price, but slightly different weight. Which one would you recommend for tour in Yellowstone NP?

Both have excellent optics. The 16x50 will be more compact and will work great. The 15x70 is very large, but able to gather a lot more light which makes them a favorite for sky gazers. If you plan to do day hikes, you'll need to relegate a rucksack to the 15x70 binos. My friend's 15x70 binos are wonderful things to use. Both binos will be hard to hand hold due to their magnification, so be sure you can rest the binos on something (car, tree, sign post, tripod). Another option is a spotting scope on a tripod. Hunting stores carry spotting scopes.

If you are looking at animals in twilight or looking at the night sky, the greater light-gathering power of the 15 X70 with an exit pupil of 4.667mm is an advantage.
The 16X50 has an exit pupil of 3.125 mm, same as a pair of 8X25 compact binoculars. So it is mainly a daylight binocular, but with more magnification, weight, and bulk than the compact model. With any binocular greater than 8X you should use a tripod. If you expect to use your binoculars handheld, get a 7X or 8X.

For land use, go for the Nikon Action 16x50 Binoculars. The Celestron SkyMaster has a 70mm lens diameter so it is not only large but heavy. Celestron designed these for astronomy viewing.