I hated the old C and C T* lenses, because the aperture changing ring is a real pain to operate. The CF lenses went to a normal aperture ring, while the older ones require you to push out on a level on the ring to move the aperture, otherwise it is locked to the shutter ring (so moving aperture changes shutter speed too). The CF lenses have a button you can push if you want the aperture and shutter to move together, but its disengaged by default, while it is engaged by default on the older C/CT* lenses. The ergonomics of the old ones are so bad, that the CF lenses were worth paying the higher prices. Also, my 80mm C lens flared horribly, and the CF one never does (the CT* is probably ok too, but never tried it).

Another consideration, if you want to get lenses other than the standard 80: Zeiss improved the 50mm lens during the CF era, so there is the original CF 50mm, which is optically the same as the older C/CT* models, and there is the 50mm CF-FLE that has floating elements. I may have had a bad sample, but my 50mm CF had terrible edge resolution, and the CF-FLE I use now is very sharp.