Isn't the global consensus that VISTA blew ass! and given the opportunity that one should to take all necessary steps to the avoid that shyt!
Every version of Windows that has been introduced since the original has been said to "blow ass". Five years from now when something new comes out everyone will be all like "this shit sucks, I want Vista back".
It depends on what you will be using it for. For just normal class work, surfing the net, and gaming go PC.
CAD, computer graphics ect... go Mac.
PC will be all you need for 99% of anything you can do on a computer. Difference is that with a PC running Windows you probably already know how to fix most things, and set it up. Plus if you want to load games on it every game known to man was designed for PC, everyone that is also compatable with Mac has issues (played World of Warcraft and people I knew that used Mac had constant issues).
Pretty much the only thing that determines speed is RAM (how much, and what the bus speed is), processor (how fast it is), and if you have multiple hard drives Raid 0 makes them work in parallel thus the hard drive can work twice as fast.
I bought a Alienware 17" laptop 5 years ago (before they were sold to Dell thank god). It is a 3.6g P4, 4gb DDR2 800mhz RAM, 160gb dual hard drives set up Raid 0, Dual CD ROM drives (DVD and CD burner/DVD ROM). It cost me a chunk of change back then but it is still kicking never had an issue and I've not found any program or games that can slow it down (I've ran CAD programs on it), and I've used it for several hours every day since I got it.