Powdr speaks truth. "Best" in this instance gets into scopes costing far more than either that the OP mentioned.
All I can say is that the VX3 from 4-5 years ago was spanked pretty good by the same-era Conquests, to my eye. It was a color balance thing as much as anything; the Leup coatings went a bit yellow in really low light and the Conquest was more blue-white. Made a very noticeable difference for me, at the bitter end of low light, in the western Oregon jungle.
A LOT has changed since then, optically, and almost all for the better.
I agree with Jeff, the Conquest was definitely better than the two VXIIIs of the same vintage and cost in low light performance, but right now both Leupies are mounted on rifles and the Zeiss is in the box. Up a little in cost are the VX-6 and Accupoint which both are illuminated and are excellent low light scopes. For under $700, I'd go Zeiss Conquest if my main criteria was light gathering capability. It is bright.
