I can speak as to why I'm still with RDS 5.5. I got into 3D with RayDream 3D. Didn't have the money to upgrade to Carrara when it replaced RDS. But, now that RDS is an orphan, I was able to upgrade to RDS 5.5 -- the end of the RayDream line. It's an awesome program with lots of great features, and an interface I was already familiar with. Now that I have enough money to upgrade to Carrara, I'm holding off until I know that it'll be supported. As for advice -- if you have both programs, I'd suggest learning Carrara. Of the two, it might have future versions, so there'll be improvements. If you're wondering whether or not it's a viable program, just look at the work posted in the Carrara / RDS gallery. Both packages can produce some amazing results. If you don't know 3D work at all, either would be a good way to get your feet wet. No two programs have the same interface, and RDS's is a bit funky, but if you get into the program, principles you learn using one will apply to any other program, even the "big boys," like Maya, Lightwave, or Max....