I'll be repeating what some have said already, but:
When it comes to cost PC's win hands down. Just no question about it in my opinion.
When it comes to stability it's not as simple as some make it out to be. It really depends on what you do. I've worked on both professionally for many years now, and the Macs start to become as problematic, or worse once you start pushing them the "wrong" way. A big reason people think PC's are inherently more stable is because they're connected to the net all the time and then download cracked software, porn etc. Because there are so many more PC's out there those writing viruses and stuff write them mainly for PC's, so statistically you're more likely to get "attacked" if you're on a PC. But if the market was reversed I'm sure the situation would be too.
When it comes to upgradability PC's win hands down. Macs are relatively inflexible.
Ease of use: well, if you're on a PC now I'd say PC. But all in all I think Macs are a lot easier and more intuitive to work on as long as you don't have to get too deep into the OS.
Quality: Macs seem to be of higher quality, possibly because they look fantastic. But I've seen so many Macs and Apple products in general crap out, or even be faulty upon delivery (or systematically flawed like some laptops) that I don't think they're all that great quality compared to PC's.
So in the end I think you should determine if money is an issue, and what you're going to use it for.