My wife and I have 20 binoculars in magnifications from 6x to 16x. The numbers of each break down like this:
6x--1
7x--5
8x--5 (including Eileens favorite, an 8.5x Swarovski EL)
10x--6
12x--1 (This is actually a Leica 8+12x42 Duovid, so could add one more to the 8x list)
16x--1
Have hunted with them all, but which to use depends on several factors, including the country, the size of the animal, and how "shy" it is. As any example, used the 6x (an early 6x30 Leupold Yosemite) to take my only grizzly, an interior Alaska bear found in pretty much wide-open tundra country. The bear showed up very obviously a mile away.
But for a general fixed-power hunting binocular I prefer 10x, both in open country and woods. In open country 10x definitely has an edge on 8x, and also in woods, where 10x can not only reveal more detail, but has a shallower depth of field, which can reveal animals by slowly "scrolling" with the focus ring. Have spotted many deer this way. But I also apparently have steadier hands than some of my friends.
I would also guess that it depends on what kind of "glassing" any hunter generally does. I am often sitting down and carefully glassing for small parts of animals, whether at 400 or 1000 yards. Some hunters only use binoculars to look at something they've already seen, especially in thicker cover.
My absolute favorite all-around binocular is the 8+12 Duovid, which can provide the "steadiness" of 8x and even more detail than 10x. It's disadvantage is weight, but even then it's only a pound heavier than binoculars many would consider VERY light, maybe even too light for steady glassing.
