all eyes are different as are all situations.
Also these manufacturers are all making several different products. your VX6 1-6x24 will have different qualities than your 3-18x52 ro whatever it is. but generalizing (all generalizations are wrong on some level):
Top end Leupy glass is going to be a touch better than nightforce which will fall somewhere aroud VX2-VX3 in my eyes. (Haven't seen the VX3i, or VX5 yet), and nightforce maybe a touch better than SWFA.
the latter will be probably be too close to call in most instances.
Unfortunately they don't let me mount them on my rifles and run around cabelas at night hunting the mounts with a bunch of fake Christmas trees around them to see which one would work the best for my situations.
That being said... Glass is only one feature in a scope and although it is the most apparent feature, it probably isn't the sole factor you should base your decision on...
