I own the Leupold Vari-X III in 4.5x-14x-50mm with Illuminated reticle. The Vari-X IIIs are very good scopes, but I do not believe that they use the best glass on the market. In my experience, I think that my Nikon Monarchs and Bushnell Elite 4200s are not only brighter, but also have better resolution.
The Zeiss Conquests are still relatively new scopes. As such, I would wait a bit until time has tested them. That notwithstanding, I read a somewhat objective article that stated that the Conquest lenses had on of the highest resolutions and brightness. In fact, it tied with the Bushnell Elite 4200 in 4x-16x-50mm.
In my opinion, I would suggest the Bushnell Elite 4200 4x-16x-50mm. The optics are bight and clear, resolution is excellent, and the adjustments are flawless. If you are looking in the 4x-16x power range, then that is the scope that you should stronger consider - and it's price is a little less than either the Zeiss or the Leupold.
Zachary