xphunter,
Sightron aptly named their turret adjustments Exact-trac. When performing a box test to test for repeatability and returning to zero, the Sightron scopes will return to the EXACT point you started at. Tested mine and it was spot on perfect. My Leupolds are not nearly as good, in fact I've gotten in the habit of going ahead several clicks then backing up to where I wanted to be, to make them function right. For some reason sometimes they seem to hang up and not move if I'm only going one or two clicks. My Sightron scope has always moved with each click.
Customer service from what I have read, being as I've never personally had to send my scope back, anything wrong with your Sightron scope and they just send you a new one - doesn't get any better than that IMHO.
Durability - I can't see any difference between the Leupold and the Sightron scopes. The Nightforce obviously is beefier and is bound to be a tougher scope, but it weighs twice as much also.
My advice is to either find somebody with all three scopes or go to a local sporting goods store. Most of them will let you walk out the door to compare the three of them in sunlight, which will give you a better real life viewing instead of trying them out under flourescent lighting. Time it for around dusk for a real eye opener. Even inside the store you should be able to see that the Sightron is alot brighter and clearer than the Leupold. I think you'll find there's not a hill of beans difference between the Nightforce and the Sightron, and the Sightron is less than half the price. I have nothing against Nightforce scopes but for what they cost I can own two Sightrons, makes it an easy choice for me.