While I believed that PCs were once better than Macs (back when OS 9 was around), now with the introduction of OS X, there is simply no comparison. Macs are just amazingly so much better than Windows than is possible to articulate with words.
That being said, since Windows has much much much more market share (and I dont whine about that, Bill Gates sucks as a programmer but is amazing at business. He could probably market bags of human feces and turn a profit - I am all for a free market, so if MS is better at business than Apple, then so be it).
Unfortunately, due to the high level of marketshare that MS has, few programmers bother to port stuff to OS X.
I would suggest that if you could afford it, to build a HTPC around OS X but do research on Linux HTPC apps, which should ALL run on OS X since its built on a Unix BSD core.
Figure out EXACTLY what programs you want, and what you need and then look for OS X/ Linux equivalents. If none are available, then go with the Windows route.
For me, there is no Mac equivalent to DVD Shrink (That works as quickly) and I would literally have spent about 100 more hours ripping DVDs with the crappy Mac software that is available. Windows apps are just better. The OS sucks, but the apps are great :)
A Mac OS X HTPC would be amazing, but unfortunately its twice as much as I could afford right now so I went with a wintel PC.