I find Norse Mythology the most exciting, the sheer realism of it mythological stories gives a better understanding of what life was like, the emotions that were built,plus the hopes and dreams of its people shined through like a beacon.
Slavish because the nordic mythology was so complex(ases, vanes, runes, the paralels plans, Yggdrasil). And celtic because of all the nature's divinities.. Oh and Egyptian!! For all the mystery around the pyramids, the pharaons, the Hieroglyph and the pantheon. It inspired me a lot for a neo-mythology that i want to intruduce in my manga project!! ^^