1) cheaper to buy,
2) cheaper to upgrade,
3) cheaper to maintain, plus
4) they have a ton more software available for them as well as
5) having a lot more hardware upgrade options and choices.
The ONLY advantage that i can concede to Apple is the "coolness" factor -- Apple computers definitely look far more stylish and "cool" than anything you can find in the PC world. So I guess if you put a lot of weight on the "hip" factor, plus have money to burn, then it might make some sense to buy a Mac. But beyond that -- it just makes no sense whatsoever. A Windows PC is simply a better product choice, period.
All that said, though -- if for whatever reasons you are looking for an alternative to a Windows PC, why wouldn't you consider a Linux PC? That would seem to make far more sense than the Mac alternative. You get the advantages of cheaper hardware, more and easier hardware upgrades -- but without whatever it is you might not like about Windows. And after all, Mac OS X is really nothing more than BSD Unix, which in turn is pretty close to Linux. I have to believe that for most users there just isn't much difference at all between a Mac and a Linux PC. So if one is really looking for alternatives to Windows, my suggestion would be something like Ubuntu Linux. It's easy to install, it has a Windows-like feel to it, and there's a plenty of software and support for it.
But still, all things considered, for the average user Windows still remains the only sensible choice. That's just good old reality these days.