The best one as far as Mac or PC is the one you're the most familiar with- so you're more likely to learn the shortcuts and so on. By the way, Lynda has the best tutorials that I've found, and even though I use a PC (and it seems all the professionals on there and otherwise) use a Mac, other posts where I wondered the same thing also mentioned it's down to preferance these days. Just invest in a nice video card and a good upgrade of RAM whatever you use...