I may be a little biased because I own a nightforce, but I don't really feel these two are comparable. I have looked through a Sightron several times (couldn't tell you the model, it belongs to a friend), but I've spent hours behind my nightforce. I feel like comparing the two is like comparing a Corvette to a Taurus. They'll both get you down the road, but not in the same way. I don't know, that's just my opinion. I don't think the glass is really comparable.
Me too. Every Nightforce I've evaluated had good glare performance, and good resolution and contrast. Every Sightron had below average glare performance and contrast. Resolution is usually pretty good with Sightron scopes, so they work fine for South facing targets at firing ranges. Between the two, I would recommend Nightforce for hunting, though.
The only Sightron line in the running glass wise with NF would be the SIII line.
Even then I think it is close enough that much of it would depend on the individual viewers eyes. I would say that the SIII's are a touch brighter maybe. I still think you get less glare and at least as good of resolution with the NF.
The issue for me with the SIII line is that you are getting pretty close in price to the NF if you get one of their new reticles, which I would want, and NF has much better features overall so to me it would be the NF all the way. I guess Sightron does have some niche stuff in the SIII line so maybe that would change things for some.