My first computer was an Imac, so of course I'm gonna vote for that, but here is a more detailed overview of my opinion:
Windows: An older computer, so there is more variety in it's versions. It is also cheaper, and Has many more programs to use, although most of these aren't the best quality.
Apple: This is a newer computer variety with sleek design, but it costs much more. There are not as much games and programs for it, although the ones that are compatible with apples are very high-quality.
MACs all the way! I have Mac OS X and Windows 7 on it. And Windows works better on my MAC then any PC I've been on. No viruses ever, and it's easy to manipulate programs on a mac. There's always a way to get Windows stuff to play on a mac too. I've done it countless times.
I'd like to say Mac since they one upped each and every field PC has SAVE ONE, GAMES. There are a lot more games compatible to PC than those compatible to Mac.