I've owned them both, albeit on different platforms.
In general, I've found the Zeiss' tend to render a slightly contrastier image, while the Schneiders deliver a gentler, less aggressive image. Both are superb.
If you're choosing between these lenses on a Rollei system, know that the Schneider is available in AF, or as a manual focus f/2, if you want to go fast. Choices, choices!