Just finished looking and shooting a 8-32 Sightron SIII, 5-22 NSX NightforceF, and the newer 5-25 ATACR Nightforce alongside my Vortex Viper PST.
IMO, the NXS isn't worth it. I liked the way the scope fills the view easily at all zoom levels, but the optics, knobs, etc aren't enough to justify the cost FOR ME. The knobs turned well and had a dull click. The parralex was a bit too easily turned but still felt tight as you would expect from NF. The newer ATACR NF has a great field of view that is larger with great glass. That was a very nice touch, but I have no idea the cost. I'd suspect it would be enough for me to cringe. Worth the money?... IMO, probably not, but it was nice to use. If you have the money I'm sure you'd love it and it's something you would keep forever.
The Sightron was nothing new to me as I've had days out using it, but compared straight between Vortex, Sightron, and NF, it's very close to the NXS, but appeared to lack a bit to the ATACR, at least in my eyes. The large view of the ATACR leads you to believe it's bright. The Sightron shares the same full viewing at all zoom levels as the NXS which I like. It's also not as susceptible to head position as the Vortex is. I find the Vortex shades the edges a bit and when you have a full view, you zoom out and it changes. That's my biggest, and likely only complaint for the Vortex. It's major to some, annoying to others. Eye to lens distance is critical, but can also lead to good head position.
For the 200$ I can see some people paying this cost for Sightron. It has a nice reticle, etc. The parallex knob is stiff, but the other knobs are too loose but still have nice firm clicks. More click than NF and Vortex. NF also has less click than Vortex. Sightron is missing a zero stop which, in my opinion, is huge. The new model that has the zero stop has a MRSP of ~1400. This then makes it somewhat comparable to the NXS, but still a good deal. 600$ (nearly double the cost of the Vortex??? ) That's up to you. IMO, not really worth it. If the 1000$ SIII had a zero stop I'd say it's a great deal, but as of now it's only a good deal, much like the Vortex for 200$ less. Vortex's glass followed up the field. It's really not bad and I was quite easily seeing hit marks at 1100yards. I'd seriously say detail is 93-95% of the other scopes, but it did clearly lack brightness. I'd say around 18-20% loss if you consider the ATACR as 100. 95% for the NSX, and 92 for the SII.. Once again, 200$ savings and not a huge issue for most of us considering the detail is still good.
Of course this is all my opinion. We were shooting in good day light, mostly sunny and 990-1100 yards. ATACR was on a custom 338 AI, NSX was on a custom 308, Sightron a custom 300W, and my Vortex on my semi factory 308.