For me it depends largely on the surrounding lighting conditions. During the day I prefer dark-on-light; in the evenings I prefer light-on-dark. If pressed to c

For me it depends largely on the surrounding lighting conditions. During the day I prefer dark-on-light; in the evenings I prefer light-on-dark. If pressed to choose one I'd go for light-on-dark, because having your retinas exploded by a pure-white background is far worse than having to squint a little to read light-on-dark during the day.