It's hard to explain why one OS is better than other with a simple post.
Have you seen somebody switching to Mac and going back to Windows?
Mac have the best combination of hardware and software. You won't see bloatware/crapware installed on a mac. You don't see neons, bunch of useless buttons, thick design... Go to a Apple Store and check an iMac, Macbook Pro. 10 hours battery life? You don't see that in competition.
It just works. Sounds subjective but that's how it is. Lets say you need Skype. Download the .DMG file (it's like an ISO) and copy to Applications folder. Want to uninstall it? Just delete that single file (it keeps a tiny preference file but it won't creep your Mac in the long run). Want to talk to somebody? Just press the Call/Video button. You don't have to worry about configuring sound, drivers, etc.... It Just Works.
Exposé. That's the first thing I miss when I'm using Windows. Instead of looking for your app in the bottom screen, you press a button (just configure to whatever you want) and you'll see all the windows thumbnails filling the screen. Just check youtube for it.
GUI; You'll notice applications on Mac are easier on the eye. Compare the Control Panel to System Preferences (on a few previous post).
Performance: Windows is a little faster on some specific apps (and specially games) but overall you'll end up preferring a mac.
Examples;
Microsoft Word 2007 open practically instantly (on my AthlonXP 2500+). Apple pages 09' takes like 5 seconds (first open). After open, both work the same way (speed).
Boot; Macs boot faster.
Opening a PDF/image/song/whatever; In a mac, just select the file and press SPACEBAR and you'll see the file instantly. On Windows, you probably know how it is.
When you buy a mac, you don't worry about upgrading as often as a PC. A Mac works the same way as the day you bought (even better with software updates). You don't upgrade because you NEED. You upgrade because you WANT. I plan to buy a macbook pro not because it has a better processor, HD, RAM, etc. Mine works perfectly fine. I just WANT the aluminum (one-piece) frame, 10h battery-life, illuminated keyboard, the multi-touch trackpad... Those are nice features, not marketing numbers. My family members buy new computers (PCs) because the older ones simply doesn't work anymore.
I could write for days, but you can have an idea reading the responses here.
Get a Mac. You won't regret it.
