Intellect - Light, I don't think I need to explain myself, his accomplishments in getting the Death Note the second time around and how it worked out was amazing.
Physically - Light is a lot more built... sort of, I mean you saw Lelouch completely out of breath when he ran around the school looking for the cat that took his helmet, Light ran around outside after getting several shots from a 6-shooter into his chest.
Personality - Light is completely dedicated to what he's doing, decisive in what he does, Lelouch still has traces of uncertainty in terms of whether or not what he's doing is right, which is shown in his encounter with Euphemia before she went berserk.
Better Main Character - Light, don't really have anything to support this, but, I suppose this is just personal preference.
Death Note vs Geass - I've only watched the anime, for now I like Death Note alot more since it's completed, and the drawing/art/animation is to my preference, while the sickly thin looking characters of Code Geass has never been my cup of tea. Story-wise so far Death Note still has it too for me, Code Geass can still prove me wrong though.