I like Japanese more. They usually do better voice-works and be in character.
And about Lelouch sounds older than he should be, I bet the director direct his seiyuu to act like that. The seiyuu is more than capable to use his 18 year old voice if he wants to, so it's intentional.

It's not like I against English dubber or anything. I prefer to watch and read everything in it's original language if I can, since there's some parts that you can only find in original versions.