Did a huge amount of comparing these to the Sightron SIII series a year and some change ago. Glass quality is very subjective, but the Sightron's glass was better in my eyes than the VX3 or Mark 4 Leupold glass, but not by a huge difference. Actually I had to take both scopes off of their respective rifles and put them next to each other to see any difference. I gave the Sightron the upper hand due to being able to see more imperfections in the 2x6 that was about 90 yards away.
Either way Leupold's glass is pretty good, customer service has been great when I had to deal with them, but I still prefer the Sightron SIIIs and have had two of them. I've also owned a couple of Leupold Mark 4s too.
Personally, if I were going to be dialing in a lot of my adjustments I'd go with something a bit more sturdier than the VX3 as well. Price is going to go up considerably, but you do really get what you pay for as far as comparative prices to comparative reliability. I've broken too many cheap scopes to ever want to put one on a serious rig again.