I love fucking mac vs pc discussions!
Well, I have both, on one machine, because of several reasons.
OSX is more stable than windows, in my 10+ years of experience with it. It's better suited working on, simply because there are less games for it, and generally you get a much superior system with less tweaking than windows. Their updating system, their integration of all things email, messaging, facebook, applications, alerts, photos..
On windows I have each and every application asking me for updates in their own unique interface, frequency, etcetc..
OSX has way better color management, something that is critical if you are working with print, design, photography or video..
No viruses. Helps a lot with stability. blah blah blah.
If u run osx on a mac, troubleshooting and bug fixing, drivers etc, are easier because many people run exactly the same hardware. Also, very good build quality on their stuff. My MBP is 5 years old or so, still works fine after years of 24/7 abuse. (Had to change fans a few times though..)