I like windows 98, yes srsly. Atm I use win7 but I was using XP for a long time. Never used Vista and never will..
XP is the most popular OS, i believe the most users will choose XP. but i like the win7 best, and i've already got used to it. Besides, vista is the worst, i confirm!!
I think that XP is only a choice when you have to deal with obsolete hardware. Obsolete hardware is everything with less than 1 GB of RAM. Vista was not to bad, only a little hungry of resources. I used it for years and I never experienced any horror story I heard. Seven is my present choice, of course.
XP is dated, if you're still using XP, stop Vista was good, but it was a memory hog 7 is the most updated version of the three, not the memory hog that Vista was, and actually up to date.
I used to like Windows XP but after using Windows 7, I prefer Win 7 over all os present in the market now.