in rhino you can round with variable adjustable radii:
http://www.vimeo.com/3275232this vidoe shows nice how you can edit rhino nurbs control points:
http://www.vimeo.com/4283768a simple tutorial how to make a twisted sweep shape in rhino3d with a few clicks:
http://www.vimeo.com/8027872here a nice little rhino tutorial how to make a design ring:
http://www.vimeo.com/7793719