I myself have always had good luck with headers. I have had the same headers on my sons Dart since we put it on the road in 1997 and it has never had a leak and they still look good. The same goes for my 63 but its only been on the road for almost 2 years.
But like was said it just depends on what you want. I like headers because I have to build cheap combo's and I need the hp headers gives me. But if someone can get the 500 hp or whatever they wany with manifolds then they wont need headers if they are happy without them.
I was thinking about getting the Max Wedge manifolds as to me they look like they might flow as well as headers. But they cost way more then my Headman's and the cast iron manifolds are much heavier. And any drag racer knows weight slows you down. Ron