So my local range had the Vortex PST Gen 2 (3-15) in stock as well as the illuminated Nikon FX1000 (4-16 and the 6-24). I was able to spend some time looking through them side by side and these were my impressions:
A few things to note:
The Nikon I looked through was the MOA reticle for the 4-16 and the Mil reticle for the 6-24. The Vortex was the EBR 2-C mil reticle.
I did not have each scope mounted. I simply put them side by side on a counter top and looked through them.
"Glass":
With regards to optical clarity, there isn't much difference between the Vortex and the Nikon 4-16. Personally, I think the Vortex had better image quality when looking outside (I was looking at sunny leaves on a tree if that changes anything). I also think that the notion of optical quality is very personal so I'll leave it at that.
Illumination:
With regards to illumination, it isn't even close. The vortex, to me, was daylight bright and on the max illumination setting, it was easy to put the reticle into a leafy tree and not lose it. In contrast, the Nikons (both of them) are not, in my opinion, daylight bright at all. The 4-16 Nikon's reticle at 16x looked very dark when put against a visually complex background. On a pure white background, I would say that the Nikon's illumination setting of 10 is about equivalent to the Vortex's 7 or 5.
I will say, though, that another reason I greatly preferred the Vortex over the Nikon's illumination was that the Nikon reticle illuminates everything. It illuminates the actual reticle itself as well as the numbers. However, I found that at both lower and higher/max magnification, the eyebox of the scopes were unforgiving such that if you were not facing directly on, the illumination would have a 'smearing' effect that made the numbers and subtensions illegible, especially in the 4-16 version. I tried adjusting the parallax as well as the diopter but to no real avail. The Vortex did not have this issue or at least not enough that I noticed it.
I'm not ruling out the fact that this is just user error on my part. Like I said, I didn't have these mounted. I only had them on a countertop and so it was challenging to get a consistent eyebox every single time when looking through them. But if it is, in fact, an eyebox issue, it could have been due to the fact that the Vortex has a more forgiving eyebox.
Turrets/Magnification ring/Parallax:
With respect to the turrets, both the Nikons and the Vortex had equally responsive turrets. To be short, they had very satisfying clicks. The parallax knob adjustment on both the Vortex and Nikons were *very* stiff, however. Maybe it was because they are new, but all 3 scopes took some serious effort to adjust the parallax. Also, with regards to parallax, the Nikon rep in an earlier post mentioned that the NRL guys could 'resolve' targets closer than 50 yards. I think 'resolve' is the right word. At the closest parallax setting, objects closer than 50 yards were definitely blurry. If, for whatever reason, I was using this for short range work, it would be a struggle.
The magnification rings on all three scopes were similar. No noticeable difference among them in ease of turning. I'd still buy a scope lever for them.
My dumb thoughts, in summary:
Again, these are my opinions so take them as just one data point.
From Nikon's website they currently seem to offer illuminated and non-illuminated reticles for the 4-16x model at $750 and $650, respectively. The 6-24x model is only illuminated and $800.
I was considering the Nikon because I'm looking for a 3-15/16/17/18 hunting scope. And while I am waiting on that lottery win to get that Tangent Theta, the Vortex and the Nikon were the two in the running. But the Vortex wins it because with both reticles, I would need illumination to be able to confidently see them against dark/complex patterned backgrounds. Against relatively uniform and bright/white backgrounds I think they would be fine. I suspect that this is due, in part, to the fact that the glass at the top end for this range of scopes is not the best and so you lose some clarity and brightness. At 15x and 16x for the Vortex and the Nikon, respectively, the reticles are too thin to easily keep track of. Illumination is what makes them stand out against the background. And in that category, the Vortex wins, hands down. As I mentioned above, the Vortex is much brighter than the Nikon.
The Nikon 6-24x, I'm also pretty lukewarm about. The 'smearing' effect I saw as well as the fact that the eyebox on the Nikons (both of them) did seem less forgiving than the Vortex does make me a bit wary. But as I mentioned above, that may very well be due to operator error on my end. But even besides that, I prefer an open center reticle with holdover markings like the EBR-2C. This is entirely personal.