LeLouche would win simply because he'd identify the greatest threats in the Death note universe and then use his identity as Zero to eliminate Light & company. After all, the Death Note only works if it has your name, and LeLouche is shown as repeatedly hiding that detail from the vast majority of people... So... :hehe

Well, that, and Light has a notebook. LeLouche has a small army of dedicated rebels in mech suits.

This is literally the epitome of the US Military versus [insert nation in Middle East here]. :lol