I'm definitely more inclined to Lelouch than to Light, but for those who say Light, please do explain. Light's intelligence feats can be great at times, especially with his plan to give up the Death Note and then obtain it once again to lower L's suspicion and all. The problem is that Light is incredibly arrogant and it has brought him trouble on many, many occasions. Lelouch is not perfect but at the same time he never made any blunders as bad as "Omg let's kill Lind L. Tailor because he's pissing me off." It's not that Light is stupid but he's got so much pride that he's like a child, if someone is challenging him he thinks to face them head on and stomp on their pride instead of taking the logical way and avoiding them for safety.
Lelouch's blunders? Always come from unforeseeable circumstances, like the deal with Euphie. That was something he could by no means could control. Light's blunders? He makes so many it's almost embarrassing.
I suppose that in a way this is true:
Since both are 2 of my favorite characters I will say that you can't compare them because they had different opponents to counter and followed different approaches.
Lelouch used guns, Light didn't. Lelouch tried to rule the word like an emperor, Light tried to play god.
Light has shown his intelligence throughout the series where he had to battle against a genius, L. Lelouch's opponents were powerful and haxed as hell so he didn't show as much.
Lelouch is better in on-the-spot decisions during the battle, whereas Light is fantastic from the comfort of his house.
Finally Lelouch won, whereas Light lost but I think that was just the choice of each of the authors.
So all in all these 2 cannot be compared, each of them would probably be worse than the other if they changed places.
The two were in such different circumstances, their situations are difficult to compare and their skills were definitely more set for their own settings than for the other.
However, I would wager that Lelouch would do better than Light with the Death Note for the sole reason that he wouldn't be drawn in to Lind L. Tailor crap and wouldn't give up his location nearly as easily. Lelouch has pride, but not enough for him to lose the battle over something as childish as him being pissed off. Lelouch knows better than that. Even if Light IS more suited to that situation, Lelouch isn't bogged down by stupid pride that would give him away. Light in Lelouch's position? Not a chance. He'd get offed quickly by virtue of the fact that his skills were never set for that, he's no military tactician and he just doesn't have Zero-style charisma.
I'd say Lelouch is superior by far by virtue of the fact that overall his feats are a lot more impressive and he gets out of a lot more impossible situations than Light did. If Light weren't so arrogant then he might stand a chance here but the problem is that his pride makes him do things so stupid that I'd wager even I could do better than he did at times. On the whole I'm not better than Light at what he did, but I wouldn't make the worst blunders regardless.