In past i have used Windows 95 and Windows 98. Currently i am using Windows XP.
Windows 7 might be good if you have enough RAM, but for my 1GB RAM Windows XP SP2 is the best. I tried once to update to XP SP3 but SP3 was slower. Right now I am using XP SP2 with Visual Effects disabled and Themes Off, for performance.
Windows 95
Windows 98
Windows (Home and Pro)
Windows Vista
Windows 7 Ultimate N
Windows Ubuntu
But my all time favorite window is Win 7 Ultimate N. . .