PC, there are a ton of reasons including Windows 7 which just came out as to why you would go pc. I will say macs dont seem to slow down as fast but if you have any hardware issues with a mac good luck working on it and if you hire someone it will cost you an arm and a leg. With PC you can easily install and upgrade parts yourself with ease and its fairly cost efficient from newegg.com or tigerdirect.com
Go PC youll be better off in the long run.