Hmmm. What are you going to do? Animation, architectural renderings ...?
My suspicion is that, having used 3D Studio, you're going to find a lot of the 3D software available for Mac underpowered or a one trick pony. One exception to that might be with Hash Animation Master, which is very reasonably priced, very full featured, and is available for a variety of platforms. However, it isn't necessarily used a great deal in the industry. For that you'd need to look at things like 3D Studio and maybe Maya and LightWave which (I don't think) are available for the Mac.
One compromise, if you like the Mac platform but wish to use software not available on it, is to run the software in emulation under Windows XP using a program called Parallels Workstation.
The new Intel-based Macs are very reasonably priced, and have support for things like virtualization. That means that with Parallels, you can run the software darned near as fast in emulation as you would just on a native XP system. It's sort of the best of both worlds - you get to keep the things you love about your Mac, and when you need to dip into Windows, you don't have to buy a new PC.
That is what I would do if I was concerned about using software which was regularly used in the industry but I wanted to stay on my Mac - I'd have an Intel-based Mac emulating Windows XP and, if I had the money, get a copy of 3D Studio.
Here's a link to a Wikipedia article listing various software packages and the platforms they're available on:
http://en.wikipedia.org/wiki/3D_computer_graphics_software
Best of luck!