ZD9 > KS9800: Higher brightness, higher colour brightness, a little bit more efficient, a lot more dimming zones (less halo effects), very natural colour mapping out of the box, smooth gradation very effective against banding artifacts from weak source material, supports 3D (but not in a good way) etc.
KS9800>ZD9: Better gaming mode, almost no visible trailing artifacts, HDR+ mode produces excellent bright details even with reduced backlight setting, higher colour gamut, samsung optimizes the picture more aggressively, which can be a good and bad thing, depending on the content, overall picture quality very comparable to the ZD9 but much better sound