The good news is - you can use both. The bad news (for Mac users anyway) is - the PC is probably better.
Here at Escape Studios we recommend using a PC for several reasons. First of all, our instruction videos are recorded on a PC, and the Maya interface is a little different on the Mac. Second, a number of free Maya plug-ins are much easier to install on a PC. Finally we run PCs in all our classrooms, because this is what students are most likely to find when they are working in industry.
In particular, the Parent Master plugin, which is very useful for attaching and un-attaching objects in Maya, is not especially easy to install on the Mac. Finally, audio playback in Maya can be troublesome on a Mac.
|The ZV Parent Master Plugin|
Still, as any techhead will tell you, Macs can be run on special dual-boot software, so you can boot it up in Windows if you prefer. And, hey presto - you have an instant PC. And Macs are lovely. I am writing this on my MacBook Pro - a beautiful machine, and I would not be without it.
Personally, I have both a Mac and a PC. For animation, I use my PC. For everything else, I use my Mac.