Comparing XP to Unix is like comparing a swiss army knife to a toolbox.
Unix is a blanket term for a bunch of unixish/unix-like operating systems and distributions, each with their strenghts and weaknesses. Even in just the Linux camp, Ubuntu has a far different focus from Slackware. IRIX is quite a bit different from Solaris. Etc...
It's what you're familar with, really.
WinXP has lots of wizards and such. Plug in a memory card from your camera, click on print, and a wizard will help you print out your pictures to your liking.
Unix will let you shot your own foot, but first you have to find the gun.
90% of the software I write is for servers and it's almost always for unix. I'm familar with unix, I can do a lot of work fast with unix, I prefer unix. But for the desktop I prefer Mac OS X (which has unix underpinnings). And when I recommend a computer for my neighbor, I suggest something with XP, as that's what he uses at work and is probably what his son uses in school. For my dad, I suggested a Mac. Safari is a good browser, he can download Firefox if he needs it, comes with Quicken and the whole iLife suite for 95% of the tasks he'll ever need to do. Far fewer virii and spyware for Mac OS X right now too.