I'd have to side with Lelouche as well.

Light has the more powerful weapon in my opinion in terms of destructive power.
But it can only go so far in getting others to follow him, may it be out of fear or religious worship.
Lelouche can mind control it, or simply gain sincere loyalty from his tactics and ability to lead.
Plus Lelouche always keep a clear and focused head on his goal, which Light became obsessed with playing and being God.

If they were to face each other though? It all depends on how well Lelouche can hide his identity like L did (Which he did right up to around the end).
If he can pull that he'll probably turn the tables on Light. Otherwise Light get's an easy victory.