Where reliability is crucial, and in tough vertical country where weight matters as well, make mine a Leupold M8 fixed 4x28, 6x36 or 6x42. If you must have a variable or must spin turrets, the only one I would consider would be a Nightforce.
I have had failures with too many variables, including several Leupolds and a Swarovski, to trust them on a back country hunt. The older Leupold Vari-X III 1.5-5x20 has a fine reputation for holding up on hard kickers, and may be the only exception to my comments above.
