My 2 cents on the subject: I don't have Carrara, but I just recently purchased RDS 5.5. I'm already familiar with the interface, so the learning curve is proving to be almost non-existent. The feature set in RDS is incredible. Now, RDS will not be further upgraded. This is the end of the line for RDS. But, (and this is an important consideration), RDS is a very powerful application and can be used to create some amazing images. Carrara is also a powerful program, but from reports here, is very buggy. I guess it's a matter of how much patience you have and what you want to do. For my own part, I bought RDS because it's stable, proven and was incredibly cheap. Good luck!