As someone who enjoys occasional birding I prefer high quality glass (Swaro spotter + binos) so my views on rifle scopes are similarly skewed towards image quality. Looking through my friend's $400 Millet LRS 6-24x56 makes me want to vomit.
I started off with two Leupold MK4s 4.5-14x50 & 6.5-20x50. Pretty good scopes, tracking was a bit suspect on the 4.5. It also had one corner which seemed a bit less clear than the rest. The eyepiece on the MK4s I felt was a letdown, it almost caused the image to appear smaller than the stated magnification. It also had quite a difference, upwards of an inch, in eye relief between minimum and maximum magnification.
Next I got a Nightforce. I loved my NXS 5.5-22x56, it had wonderfully reliable tracking and build quality, however the glass was a touch disappointing for the size of the objective. Dull, not much contrast, moderate chromatic aberration and had some of the longest minimum focal distances I've seen in a scope. Turrets were a pleasure to operate.
Today I own two Leupold MK6 3-18x44 (had 3, sold one) for their size they perform exceedingly well. For all of its positives, there are areas which I do not like. The glass is crisp and clear all the way upto about 16x. After that CA creeps in somewhat and the image gets noticeably, but not significantly dimmer. The CA is induced by location of the pupil away from the center thus CA can be reduced with perfect eye placement. Although close, I wouldn't consider it on par with Alpha glass. The parallax turret is stiff, coupled with its low profile makes for more difficult operation than I like. The knob is fast, only 180 degree turn. I prefer those which offer a bit more sensitive adjustment.
Anyway, those are my opinions about the NF and Leupold scopes I've owned. If you want any more details on glass quality feel free to send me a private msg.