OS X is my OS of choice.
It has the stability of BSD Unix along with access to the "underbelly" if you want to get there, but has the ease of use and nice GUI of a consumer OS. There's also a great selection of software for it, and you can actually run "real" productivity applications like MS Office and Adobe CS(before anyone says-Open Office is not a substitute for MS Office, and Gimp is not a good substitute for someone who knows their way around Photoshop). I don't have to be on the cutting edge of games, so the ones available for OS X are more than sufficient for me.
Granted not all is perfect in OS X. I regularly use and maintain systems running 10.4, 10.5, 10.6, and 10.9(although I have systems running ever other version). At least with towers that actually have expansion slots, you have to be VERY careful with expansion card selection. Basically, if you pick the right hardware it will work seamlessly and is the very definition of plug and play, but if you don't pick correctly good luck getting it to work. I've found this to be true with things like USB and WiFi cards.