Beauty is in the eye of the beholder, I suppose. IMHO XP looks too dated, although its Silver theme isn't too horrible. Vista looks like some half-breed kludge, although it was okay for its day. 7 looks great, professional and modern with its translucent borders and gradients (once you tweak a few settings), and 8 is even worse than XP - flat, dull, lifeless. They've even removed such basic things like being able to adjust icon spacing... unless you want to use a registry hack. :p
But this is the kind of question where you ask 100 people what looks best, you're going to get 101 different answers, LOL.
