Per Ed Pawlowski:
... I'd go with W7. I find it a bit
better than XP.

+1, but with the observation that I have 8.1 on my laptop and, since
installing something called "Start8" and tweaking a few settings, it
looks/feels pretty much like Windows 7 - i.e. it's 100% livable for me.
--
Pete Cresswell