I've always been a fan of Rhino, but fairly recently converted to PowerSHAPE from Delcam. PowerSHAPE, like Rhino, has its roots in surface modelling and I find it much more powerful than Rhino in many areas. The downside has always been that it is a lot more expensive than Rhino. However Delcam have just announced (wish I'd known) a new version of PowerSHAPE called PowerSHAPE-e, which is completely free (see
www.powershape-e.com). Like all free things, there is a catch - you can design all you like (including unlimited saves) but when you want to manufacture from the model you need to export it and at this stage you pay a fee to export or convert to the full PowerSHAPE version. Nonetheless, it is a cheap and easy way to get going with the product.
I think all you Rhino lovers should download it and have a play - I think you'll like it.