Mac OS X is by far the easiest to use and is probably my favorite. Linux is nice once you get it all setup but the setup itself can feel like a chore. I dual boot Mac OS and Ubuntu on my Mac Book for everyday use, Windows XP is only installed on the pc for games. Gotta have my COD4.

I personally run a lot of different Operating systems, they all have some pros' and cons' for sure.

I prefer XP Pro, and I'm seriously diggin windows server 2008

I wish the Mac OS was more unix oriented then it advertises.  If you are a unix user and think you are going to drop to command prompt 'su root' and make some etc/password changes think again.

I did find a great book Mac OS X for Unix Geeks, good stuff.

http://www.amazon.com/Mac-OS-X-Unix-Geeks/dp/0596003560/ref=sr_1_13?ie=UTF8&s=books&qid=1215023550&sr=8-13