I am a Vortex dealer and have the 20x56 Kaibabs. I previously owned the 15x56 Kaibabs. The 15's were definitely more comfortable to look through and were brighter, even though Vortex improved the coatings for 2014. These definitely require a more stable tripod or mounting platform; however the added magnification is significant and greatly minimizes the need to break out my spotter. I look at a lot of deer in all lighting conditions and the Vortex 20's hold up very well compared to my Swaro's, Leica's, and Vortex Razors. The others offer a more pleasant viewing experience, but it is mostly due to magnification. The magnification definitely reduces the exit pupil and bright image; however, it magnifies the animal enough to still see some detail down to legal light. Looked thru the Zeiss 15's at a trade show and they looked good, but indoors and handheld, if I remember correctly, so not a fair evaluation. Hope this helps.
