I had bino pairs of both sets. I felt it was a bit redundant having both sets and I obviously had a lot of money tied up in them. I became quite interested in planetary and lunar observing and consequently my scope collection started to feature longer and longer focal lengths.
Having read about the development of the ZAO first generation ep's, I discovered that they were originally created to optimize the Zeiss APQ line- with focal lengths of f/8. Of course, they would optimize any focal length but they were made with the APQ series in mind. As a previous post mentions, the ZAO II's are optimized for faster scopes, but of course, excellent for all others as well.
As my focal lengths went up, f/8 - f/20 for my planetary specialists, it became an obvious choice to stick with the first generation ZAO's for me. I guess I am a purist.
It should be noted that the CZJ's are also excellent, and they were optimized for f/10 according to what I read, but again, they are terrific across the board. The 16's even beat my ZAO II bino pairs on the moon one night when I compared them - more contrast and detail seen on that particular night, under that particular sky (tmb 100/800).