The Vortex offers nicer turrets, illumination, and the option of a MOA based reticle. For $200 or so more, though you can probably find it closer to $800 by calling some of the scope specialists (try Liberty Optics or Sport Optics; I know Sport Optics is currently offering a set of Griffin ETAC rings with any Viper PST, and those rings normally go for $125).
SS is made in Japan, but NOT at Japan's best optics factory, while PST is made in the Philippines at their best optics factory. Vortex is known for a terrific warranty, although SWFA is reputed to be excellent too. The SS glass is getting rave reviews at snipershide. Personally I would go with the PST, but they are very close competitors.