oohhhh this is going to start a flame topic.
Macs and PCs are both very good if you make sure to use them correctly and pick the right one for you.
I know of many photographers and graphic artists that love their PCs, and many that love their macs. At this point it's more about your personal preference than one going 'faster' than the other. if you are very sloppy in your computer's security and upkeep, you might want to consider a mac because it has more leniancy for that type of thing. If you are good with security, that's more of a non-issue.
I personally like PCs because of the layout and file system, which I have gotten VERY accustomed to. I've used macs a fair amount, and while I like some things about them, the setup and such is too foreign and I don't have the time to learn it all...I also like the fact that you can upgrade/modify a PC, which you can't do with macs. I just had a custom built PC made several months ago for processing and heavy work, and it's working amazingly without any bugs or viruses or spyware, malware, anything. Not to say that PC's can't get bus and such, but if you keep them up right it's not a big deal at all. You need to make sure to get top quality parts, too. Many big companies like dell and hp make fairly nice systems but use cheap/dated parts, making them less reliable. if you build your own or pick the parts and have someone else build it (like
www.monarchcomputer.com), you can get a much nicer rig for cheaper than buying it from a big company.
you should try out an imac at an apple store. if you like what you see alot, look into getting one of them. they are high quality machines.