I have both a Mac and PC. I like both. They are different and both have pros and cons. I don't believe one is ever really "better" than the other, because it just depends on what you need it for.
Along with what's already been said, a lot of software is default made for PCs. Only when it comes to media software (graphics programs, video editing, etc.) does the software selection tend to favor Macs. Valve is pretty much the only game company that makes decent games available for Macs, so if gaming is important to you, a Mac is not the way to do it.
There are options for being able to run both Windows and Mac on the same computer, similar to what Timmy said. So if you're into multimedia and really want the Mac but need the PC for games, there is software out there that allows you to use both.
As for viruses, the Mac is definitely superior. Yes, Mac viruses exist, and you should protect against them, but there is no question about PCs or Macs having more issues with it. I've been using my Mac for three or four years and haven't caught a single bug; with the same kind of use, my PC is always getting stuck with one thing or another. I like not having to stress so much about keeping my computer clean.
I also personally like the fact that my desktop Mac is entirely contained within the monitor. It's certainly less customizable, but I like not having to make space for a tower. It suits my needs.