Both are good scopes. It just depends on what you want and the features that you like. I prefer a scope with a fast focus ocular, constant eye relief throughout the power range, etched reticles, clean and precise windage and elevation adjustments, clean and clear sight picture all the way out to the edge of the viewing area, and optical performance in low light (specifically contrast between the dark colors). I don't really care too much about weight as long as I get the best optical performance in the price range. The Zeiss Conquest meets all of those criteria for me. The Leupold would work for me, but there are a couple of areas it falls short (specifically the eye relief is not constant throughout the power range, all reticles aren't etched, and contrast of dark colors at low light) compared to other scopes I have used and looked through. The only Leupold scope that would meet my personal criteria would be the VX6. IMO, The VX6 is on par with the Conquest. I just refuse to pay $400 more for a scope to get the same features I prefer and optical performance.
Another scope you may want to look at is the Minox ZA5. That is one heck of a scope.