I've not used Maya for Mac, but I have used many other art applications, such as Photoshop, Illustrator, and the like. Aside from a few keyboard shortcut differences, I've never noticed much of any difference between the performance of Mac and PC counterpart programs.

My only real reason for having a PC is that I do more than just Maya and art related stuff with it, and PC just has the largest "area of influence" so to speak with all the software out there.

So, I reckon you should get whichever you like better.