For me, it's Ubuntu and it is since the days of Ubuntu 7.04 when they used to provide a free live cd distribution. Good old days!! When I started it was dual booted with windows but later that love grows and now its only ubuntu!! Its on my home server and laptop both!! After almost nine years of daily use for programming, photo editing and kernel development, now this Unity desktop feels like working eyes closed!! I loved Ubuntu just because of its ease of use!! I can tell lots of advantages (dis-advantages also) about ubuntu now, but at the beginning it was just look and feel!!