I develop prototype military optics for a living and over the years I've developed a quick method of assessing riflescope quality. I just got back from the SHOT Show in Las Vegas. I spent a fair amount of time inspecting Vortex and Hawke scopes, among others. I evaluate glare and chromatic aberration over the entire field of view, and I take detailed notes. I can only do a limited evaluation, however. I do not have the opportunity to do quantitative optical tests, which would include veiling glare, chromatic aberration, resolution, transmission and reticle adjustment accuracy and repeatability. I've been doing this at SHOT for the last four years. After a while, some trends become clear.
I can say with confidence after looking at most of the scopes in the Viper PST and Hawke Sidewinder lines that, optically speaking, they are not in the same class. The Hawke scopes are much better. I'm not saying the Vortex PST scopes are bad optically. They are acceptable quality for that price point. However, "acceptable" is actually below average.
The Hawke Sidewinder and TAC scopes, on the other hand, are exceptional for their price point. Glare performance is good - substantially better than average for that price point. Off-axis chromatic aberration is excellent and rivals that of the best scopes I've inspected.
In my experience, if glare and chroma are good, then overall contrast ("clarity") will also be good. Lens surface figure also plays a role, but that is a material cost issue and since both lines have similar prices, they should have similar material costs. Even though Hawke scopes are made in China, the company has factory quality under control. Return rates are less than 0.1%. Hawke scopes also have a reputation for handling recoil very well.
I know there are a lot of Vortex fans out there. Vortex is a good company and they offer some features (like FFP reticles) not available elsewhere at the same price point. There are other factors than optical quality that go into a purchase decision.
Optical quality has a high priority for me, however. I would give up features before I gave up optical quality.
BTW, I have no business relationship with either company. Nor do I own a Vortex or Hawke scope.