Natural Gas and you CANNOT tell the difference.
Let me in on the secret, because I can. Don't get me wrong, you can get a good flavor with gas, given the right technique, but it doesn't match charcoal, and especially not charcoal and the appropriate wood chips or chunks. Even adding wood doesn't quite make gas equal charcoal. It is close though, and there's nothing wrong with gas, it's hard to beat for convenience and efficiency.