As film makers your glass is the most important thing in your arsenal.
Depending on our clients wishes we tend to use our Canon L series lenses but when the project is right we will get hold of some Zeiss Prime lenses (sharper than Canon Cinema lenses but also 5 times the price)
After playing with the C-Lenses at the recent BVE in London and actually getting to shoot with them on a recent shoot we are seriously considering the Canon Cinema lenses and maybe a new Canon C300 to go with our C100 kit.
Here is a great video on the difference in quality when it comes to the Canon C lenses.. might make your mind up.