I think experts in both softwares would say they're both powerful and have their strengths and weaknesses (although I'm not skilled in either). A7 is brand spanking new and is having some growing pains with bugs and stability but patches are on their way. A pro version of the software is due out later this year. We have no idea what it will have inside it. Rhino is mature and can do a heck of a lot of magic tricks. From reading through tutorials for both, they look like the learning curve is significant for both. Your taste in 3D conceptual design, your needs, and the way your brain works are the things you should consider. If I were you, I'd see if I could get freebie trial versions and simply give them a whirl. Pick something simple but useful to build in each and see how it goes. This kind of question is tough to answer. I was pretty much where you were about six months ago and I chose the A7 path because if its connection to Carrara and for the power it appears to have. I don't really know how it rivals Rhino but I do think it can build models that are good enough for me. Good luck! -Kix

-Kix