Both are good and Pros like Boyd Coddington will use both but when the factory used lead it was to cover panel seams which require thickness to cover. That is the downside of bondo. You can't expect it to hold up if it's used thick or you fill a seam because it will shrink and that seam will show in about a year.
It was designed to fill and smooth out minor flaws and not be something that creates a whole new contour.
Applied correctly bondo,or whatever you chose to call it will last and you don't have to get out a torch to use it.
Dan
