“PC or Mac?” Seems to always be a flame-war-bait issue for some folks, but in the real world of computer graphics … or any other sort of resource-intensive computing … I daresay that it isn’t really an issue, never was, never will be.
You use what you’ve got. Or, what your new employer’s got. Or what your client’s got. And if you’re working in something as computer-intensive as CG, you’d better be ready to encounter some Silicon Graphics gear too. And maybe a mainframe. The odds are really good, in fact, that you’ll find all types of equipment, all being used at the same time.
So, if you get a chance, try to spend some time on different types of machines. It’s very educational to, say, compare Blender running on a Windows box to Blender running on a Linux box to Blender running on a PC. It would be very realistic to try to set up a situation where a machine of each type is working cooperatively with both of the other two on some job. Your very own tiny, multi-platform render farm… it can be done.
What you’re going to see is that all of these machines are, at the very same time, both very similar and very different. Until you actually put yourself into that situation, it’s very hard to describe exactly what I mean. So, make it your business (if you possibly can), to put yourself into that situation. Put any flame-war biases firmly in your pocket, or better yet in the nearest trash; you don’t have time for such nonsense. You have too much to learn.
You can be certain … absolutely certain … that a company which is currently using one type of equipment is never going to “switch,” especially if they are busy on a multi-year CG project. Ditto if they are contractually obliged to make sure that their deliverables will run on client-machines which are of thus-and-such type. Since they are never going to change (and for compelling business reasons… not stubbornness nor ignorance), you must be prepared to adapt. Quickly.
If you possibly can, make this part of your CG self-education. It will serve you well.