Even though I hate these sort of threads more than anything in the world, I always end up biting... Ive had quite a few of each (15+ ATACR scopes and at least 10 Gen 2 Razors with a ton of PSTs here and there), so ive been able to nit pick on each.
Glass - Its a wash honestly, both are wonderful quality and very bright. I see my steel target at 1 mile plain as day through either my 5-25 ATACR or my 7-35 ATACR, and the furthest I used the Razor stuff was 1100 yards, which also didn't have any issues
Weight - Any way you compare them, the Razor stuff is always quite a bit heavier than the NF stuff (5-25 ATACR is 38 oz and 4-27 Razor is 48oz, or 4-16 ATACR is 30 oz and 3-18 Razor is 46 oz). If youre sitting on a bench or don't carry your rifle, it likely isn't an issue... if you do, 1 pound of weight adds up quickly, especially if you have a lighter rifle.
Features - While they are all similar for the most part, NF does edge out Vortex on some simple things that will cost you money with the Razor.
*PTL (Power Throw Lever) is standard equipment on the Nightforce with a very attractive knob that can be installed on the mag ring
*Nightforce has a much better (in my opinion) Zero stop setup that can be changed at any time, and much easier to adjust
*Nightforce includes high quality rotating Tenebraex flip up covers
*Nightforce has greater Parallax adjustment with the new 7-35 going from 10m to 900m before going to infinity
*Nightforce has a better digital illumination setup with dual colors and extremely easy to use power/intensity settings
Warranty - Ive had to send back two Razor products and 4 Viper PST products for factory defects not caused by me, or any sort of inflicted damage, with two of them being broken out of the box and going right back. I have yet to personally see a Nightforce scope (over 25 owned between ATACR and NXS) ever fail or need any sort of repair. In Vortex's defense, they were very prompt about sending either a new scope, or repairing the old one, however it is quite disappointing to get the scope in and plan on going to the range, only to find it has to go back for repair first. While Vortex may have the industry leading warranty, the best one, in my opinion, is the one I don't have to use.
Price - You get what you pay for. Nightforce isn't cheap, they don't offer discounts, however if you compare some of the above features they include, that the Vortex does not, it does bring the price closer on the two. I am not discounting the quality of the Gen 2 Razor stuff as those are fantastic scopes with no real competition in their price range, however I do feel the Nightforce easily justifies their pricing difference, especially when comparing the optics that are more expensive, yet may offer significantly less.
Quality - As some have stated, and I will repeat, the Nightforce quality control procedures are pretty incredible, if not industry leading. They don't have "cheap" models or discount scopes to compete with lower end stuff, they have a significant amount of Military and LE contracts with their products, and as far as durability is concerned, there isn't a person on the planet that will question how tough they are, or their ability to withstand severe punishment, and still function at 100%.
Resale value - look through the ads on any forum and let that one speak for itself. Its very rare to see fire sales on Nightforce products.
With everything stated, I am still a Vortex fan and very much like their Gen 2 1-6, and would have no problem owning a Gen 2 4-27 (I think the 3-18 is a bit ridiculous in size and weight for the lower magnification it offers when the comparative market of the ATACR 4-16, Mark 6 3-18, and other mid range scopes are a pound or more less)... However, when given the choice between the two, I sold my Razor spotting scope and other Vortex products for Nightforce, and haven't looked back. Vortex and Nightforce may be the last two "innovative" companies left, who strive to give the public what they want, so I support either over the competition and honestly say you cant go wrong either way.