Choose the best tool for the job at hand. I mostly use desktops, and my main OS is Mac OS X. I chose this because the GUI rests on top of a pure unix layer, and I need unix as well as linux for some of my scientific work. Whereas I get most of my work done with OS X and unix/linux, there are some apps that I use that are written only for Windows; for these I either use a VM or a dedicated PC running Windows. When I travel, I use my 11-inch Macbook Air, which has served me very well, especially owing to its portability.