Two of the most popular are Rhino and Zbrush. Rhino3d is PC only, but it is a very stable program. I'd think it would run on a Virtual PC, but you might want to ask at the Rhino Forum to see if anyone over there runs it on a MAC. It can use .ai files, does import 3DS and DXF and there is a freeware utility that will convert from .obj to native Rhino format. It can export to .obj format. The McNeel company (maker of Rhino) is a very responsive company. (I had the pleasure of taking a training class at their headquarters; they're really nice people.) There's also a very active and knowledgeable Rhino forum here. Zbrush does have a MAC version as well as a PC version. I can't tell if it reads .ai files but I know it can read .obj and .dxf formats. Zbrush is said to be quirky, but not difficult to use once you get used to it. (I don't have the program, but I know it's popular for Poser morphs.) From what I've seen, Pixologic is also a very responsive company. Hope this helps.