I've got Vista and hate it because of its bloat, I've not tried anything newer than that. I prefer XP.
I love design and visualization of Windows 8, but I love to use XP because of more fast and comfortable..
Windows 7 64 Bit for me Windows XP second choice Windows 2000 Windows 98SE Problems i have with Windows 7 has to be it's mouse acceleration curve, loved XP's much better.
Windows 7 is definitely the best Windows OS I've encountered. Vista never performed that well for me, and Windows XP was good but definitely not as user friendly as 7.