Well I think the idea of pitting them against each other isn't very fair in Light's case. Of course Light would lose if he was up against the power of the Geass. Instead I'm gonna base who would win in terms of their intellegence. With that said, I think Lulu would've died a long time ago if he was in Light's situation. He's nothing without his precious Geass. Light on the other hand would dominate as always if he was in Lulu's situation. He even demonstrated that he doesn't need the Deathnote in order to get the upper hand in a situation. The only reason Light died was because he gave his minion too much freedom and the guy wasn't as smart as he was (I mean seriously, the dumb fag put the deathnote in a fucking public gym locker).