Mac OS. I was a Mac guy from way back. I was a Sys Admin and used PCs back in the day (read: windows nt), but I always preferred Macs. They're easy, elegant and give me no troubles. I am also an Apple Certified tech, used to do installs, tech support and even full-blown network installs.
If I had the time and money, I'd get a box and install Linux on it just to familiarize myself with it, but my career has moved away from Tech these days.
If I had the time and money, I'd get a box and install Linux on it just to familiarize myself with it, but my career has moved away from Tech these days.