Never looked through a Z3, so I can't compare one of those to the Vortex or the Z5.
The Vortex is a nice scope. Just not up to the Z5. So much so that it was hard to be happy with it, in comparison to purchasing another Z5.
I purchased both of my Z5's off FleaBay. New but at discounted prices. So far so good. No repairs or warranty work required after 5yrs with the one and 3yrs use on the 2nd one. They're both mounted on rifles with muzzle brakes. Seem to be solid even under reverse recoil. Tracking has been spot on.
Didn't have the Vortex mounted long enough to really put it through the ropes. Sighting in and one hunting trip.