After using the CityBike service here in Vienna for over two years, I feel I have some wisdom to impart on the subject, and as such, here is a handy guide to the various CityBikes available at every station. Please click on the image to magnify!
The main lesson: Not all CityBikes were created equally. And free stuff should be perfect.
More info about CityBikes Wien at http://www.citybikewien.at/