A Mac is a good computer, if you want to be severely limited to that hardware. If you want to play a game that requires newer hardware, then your out of luck. You'd have to pay through the nose to get just one small thing upgraded. A PC on the other hand is easily upgradable. Everything works together.
A Mac has excellent protection from viruses, but that's mainly because it's not that popular. And don't believe the commercials about it not crashing. I was able to crash 5 Mac laptops in a month just by using it normally. And the security for the OS sucks. My own high school had Mac laptops, and they set it up so that only certain programs were able to run, a white list so to speak. I found 3 different ways of bypassing that and running whatever I wanted on there.
A PC is more compatible with every program out there, as it is more popular, but that also means more viruses. But because of a PC, you are able to upgrade the hardware, unless it's a laptop, in which case you'll have a hard time doing that. The security on a PC depends on the software you have on there as well as how you use it. Don't log in as an administrator. Instead have a rarely used admin account that you know the password to, so that when you need to install something and it requires admin privileges, you just enter the password and you are elevated for the duration of the installation.
All in all, it depends on your preferences. But you still need good security for both. A firewall, virus scanner is a must no matter which you are using, malware scanner (spyware, adware, rootkits, etc), and you should never run as an admin unless absolutely necessary, like when installing programs.
Also, just to note, if you want the look and feel of a Mac without having to be restricted, just get a Linux system, like Ubuntu or Fedora. A mac is just a proprietary Unix system, while Linux is Open Source, and thereby the community updates it very quickly. You will need to know some basic functions and commands, as it is a little advanced, but then again a Mac would have the same things if you were wanting to install and run system utilities. And you can install it on a PC, beside Windows, through a dual-boot method.