I think these two if they actually met each other would become pretty good friends. Lelouch would be the great leader and Light will be the law enforcer. Although if you ask who I like more I'd have to go with Lelouch.

Lights power is far more efficient and easier to use not too mention that he doesn't have to be there in person unlike Lelouch who needs eye contact. Light can also use Ryuk to his advantage and I just think Light was shown to be overall more intelligent with how he used his power and how he thought ahead.

Yagami-kun's power with his Death Note is most likely easier to use and he doesn't need eye contact he just needs the person's real name and face for it work Lelouch's geass requires a little more than that so I imagine Light would win but you never know.

People forget that Lelouch's real name is Lelouch Vi Britannia not Lelouch Lamperouge and he is also Zero. For Light might have a difficult time finding out his name

Lelouch! The only way Light could win was IF he knew Lelouch's name. All Lelouch needs is eye contact, so I'd say he has the advantage.