It really all depends on what you'll use your computer for. If you like simplicity and the union of hardware and software, go for Mac. Macs are very nice if you're the kind of person that doesn't like having to deal with hardware upgrades and mess around with stuff like that. However, Macs are considerably more expensive than their PC counterparts. For that extra cost, you get superb hardware, and 99% of the time you get software support for at least 3-4 years. My Late 2008 Aluminum MacBook is still chugging along, running the latest version of OS X (and will receive 10.9 when it comes out), and has never failed me. It also runs freakishly quiet. Anyway, based on the usage you posted, I'd suggest a Mac. Creative stuff like that is mostly suited on the Mac platform, and programs for that kind of thing are generally better on OS X. Most video editors and sound editors that I know of use Macs. Laptop-wise, you can buy either a MacBook Pro or an Air, but that's a whole new discussion. Desktop-wise, you can either go with an iMac, a Mac mini, or if you need tons of power, a Mac Pro.
Windows PCs are more for the kind of person who is OK with digging around into their hardware. Let's say you want to upgrade your CPU because you want to edit some super-intensive stuff. Simply buy a new one (notwithstanding socket limitations) and pop it in (desktops only, obviously). With Windows 8, Windows is actually very streamlined. It's not nearly as much difficult to maintain as it used to be (installing drivers and such). I quite like it. Laptop-wise and desktop-wise, the choices are endless, making it much more flexible for you and your budget. PCs are almost always cheaper than Macs of the same hardware, so bear that in mind.
I don't know much about Linux, but I probably wouldn't suggest it based on editing software available for that platform
To make your choice, I'd suggest trying both out first. Go to an Apple Store or try out a PC anywhere, and good luck.