I have both. To me glass is comparable. Leupold 3.6x18 is much lighter weight. The difference between 44mm and 50 mm objective is not that much. Zeiss S3 4x25x50 has red & green illumination which is nice. Price, if you qualify for Mil/LE is comparable. I also have a Leupold Mark 5 5x25 and a couple Mark 4 8.25x25's and really do not miss the extra magnification if the scope is going on a hunting rifle. I know lots of people knock Leupold, but I have used them for over 30 years (more than 16 scopes) without any problem. I think they are equal value. Look at both and purchase which ever one you like better.