Got to be honest - not used a PST and only seen in passing.
As a personal view I think there is a price bracket consideration. Every Vortex I have seen has been good, the Viper HS range is great for its price in particular. I've not had much to do with Vortex gear up in the £1000 plus range for example ( if one extrapolates it should be fantastic ) - but if I was budgetting in that ball park then the big three - Swaro, Zeiss, S & B etc would be getting the nod - if only because those brands will hold value better.