PC. I grew up on them, and know them well, and while I have nothing against macs, I gladly use the ipod and stuff, I prefer to stick with what I know in pcs, I know how to upgrade their hardware and I know all the keyboard shortcuts I need to. From what I hear, (and I know its not as bad as the internet makes it seem) upgrading a macs hardware is a real chore.
As a console gamer who detests keyboard and mouse for interacting in a 3D environment, gaming is utterly useless to me as a reason to just a computer.
I made the jump from XP to OS X (Leopard at the time) and I've never looked back. Its quirks take a bit of getting used to, but the simple things, like the bar on the top always having File, Edit, etc up there makes finding what you are looking for far easier. iTunes runs far better on Macs, and it works fine for what I need it for, (shuffling music and changing what's on my iPod.)
I have a copy of Windows 7 running as a virtual machine for the few things that I need a PC for. Now that I'm out of school, its mainly for VisiPics. I used to need it for 3DS Max and .NET, but I don't use either of those anymore. Its a fine system, but my Mac is 4 and still runs fine. I might have considered going back to PC for my next one if not for Win 8.
Which brings me to what I like to bitch about more than Mac/PC. The mobilification of computer OSes. This is a complaint about both OS X (Lion/Mountain Lion) and OS 8. Both seem to sacrifice function for form. Lion has buit in redundancies, like the app window when the Dock still exists. 8...I've only dicked around with for 5 minutes at Walmart, but I couldn't figure out how to minimize a window, so there's that.
Just...keep your tablet away from my laptop. If I want a tablet, I'll fucking get one. (that probably runs Android.)