Ever have to listen to a bunch of nerds fussing about which OS is best? Get's a little old, don't it? To put an end to all this silliness, here's a definitive* guide to the pros and cons of the three major flavours of OS.
Pros; pretty, have a really cool magnetic power charger thingy, and aren't as crippled by lack of cross-platform supports as they used to be, designed for use by "artists" ie people with no common sense or deductive reasoning skills. Theoretically more "intuitive" although it's largely a matter of what you're first exposed to.
Cons; roughly twice as expensive for equivalent screen size and processing power, single source everything (so if Apple doesn't offer the configuration you want you're screwed), not commonly accepted for business usage except in certain graphics design fields. Mac users will point out you can use Parallels to run Windoze OS and hence proggies: however, if I want to dual boot or virtual box I'll get twice the machine in a pc and run OS X parallel. Mac groupies (and they tend to a cult-like devotion to the brand, almost as bad as *nix fanbois) always brag about how great the security is for macs. This is because no one cares enough to write malware for macs http://cad-comic.com/comic.php?d=20060513
PC's w/ Windoze
Pros; far cheaper than macs (can be anyway, Alienware etc are still obnoxiously spendy), options as to supplier (freedom of choice is good), most widely accepted OS (depending on version).
Cons; Microsoft is pure undiluted evil, Win* are all memory hogs to some extent, Vista is the software equivalent of a prison gang rape, the many suppliers can lead to weird conflicts and driver issues, piss poor code results in security holes any 13 y/o script kiddie can exploit (these can be eliminated by following good opsec procedures, but there's less room for you to do something stupid and get away with it) and did I mention M$ is basically a James Bond villain?
PC w/ *nix
Pros; far more secure (and yes, a lot of this is due to obscurity like Macs, but a lot is due to the community being involved in patching), updates and drivers etc can be easier to manage, free free free!
Cons; annoying fanbois who treat their OS like a religion, steeper learning curve, DIY, can't use all programs (Quark anyone?), some minor formatting issues with the Open Office version of Word, bad for gamers.
Get a Mac if: you have extra money, you're pretentious, you do lots of video or music editing, you visit a lot of shady porn or gambling websites, your career plans include lots of time on unemployment while "suffering for your artistic vision," or you are a filthy hippy trying to buy some anti-establishment street cred. Politician equivalent: the Obamessiah. A lot of great marketing, a lot of double-talk and BS, doesn't live up to the hype.
Get Windoze if; you worship Satan, aspire to be a soul-less corporate drone, want to be able to use the standard Office programs without screwing around, are ready to exercise some restraint in what websites you goto and what you download, don't want to learn Mac's.... "Unique" little quirks. Politician equivalent: Teddy Kennedy. Powerful but works as a fluffer for Satan.
Get *nix if; you've ever attended a Sci-Fi, fantasy, or anime con (bonus if you were in costume), have another computer available to Google why the *nix box is borked, are fairly competent, don't play many video games (or don't mind running a virtual box w/ pirated *doze), enjoy playing with computers. Politician equivalent: Ron Paul. Some great ideas, some terrible ideas, never going to be as big as the fanbois would hope.
*Disclaimer; "definitive" is used in a playful post-modernist sense to mean "Random largely unsubstantiated claims that may or may not bear any relationship to the facts."