OSX
I recently sold my laptop, after years of using Windows and Linux OS's, and bought an Ibook. I couldn't be happier. It's just as stable as Windows XP. Every device I have works, including an inkjet and laser printer, IPOD, and digicam. I don't have any driver problems. I got MS Office X for compatibility, and the rest of the software I use was built in. IPhoto, Itunes, Imovie, Calendar, and Address book are all superior to any built in Windows XP software. Mail = Outlook Express. Netscape runs really fast on the Ibook, but I can also use IE and Safari. Software Compatibility actually works on Mac OS X (I can run any program from the old mac os's). Windows XP software compatibility never worked for old dos software. Stability so far is a tad better than Windows XP, which I suspect is due to better drivers. Expose is a better screen management schema than on any other OS I have ever used. The built-in Airport wireless is on par with Lucent/Orinoco, and certianly better than the Intel wireless crap I had on my old Sharp Actius. I really cannot think of a reason to go back to a Windows box at this point, not that I have anything against Windows OS. I use XP all the time at school.
The only thing I don't like is Window maximize and minimize, which I think could have been done a little better.