You'll always make better scope choices if you focus on the functioning, fit into your shooting system, overall value, and THEN price(dead last).
Like BillR I have both, and agree that weight is the biggest factor between them. -Weight is a show stopper for my hunting systems. Mk4 wins there.
-Another NF issue(to me) is the turning eyepiece. This buggers up the flip-up scope covers(which I must have), getting them in the way of bolt operation. I also don't like that NF hasn't produced their own flip-ups, like Leupold did with there awesome Aluminas. Mk4 wins again.
-NF reticles are fantastic, and IMO leupold has always failed in this regard.
NXS wins there.
The glass is equal between them, with neither dominating in resolution, nor brighter that I've seen. There is no advantage to 56mm(causing higher mounting) with this glass. Both scopes adjust/repeat perfectly. But there has been chatter about NF MOA not being 1.047"/100yds, while the MK4s definitely are.
I haven't tested this with NXS because they're too heavy for hunting anyway, so for use on my target guns only. But I test every MK4 to level the adjustments.
IMO Mk4s are superior to NXS.
But in the past couple years Leupold has caved to the tactical mob, and I don't know if Mk4 scopes are still practical for hunting.
As far as price? Well that's all being driven to stupid, again, by the tactical mob..