Headers vs. manifolds

as you can see headers have 2 distinct opinions.Some will argue they don't help much and can cause a lot of grief on a street car.The other camp will argue all day... extolling their virtues.
As always it's the combination of parts and how everything works together...I think for a 318 on the street through full length exhaust there are better places to spend your hard earned cash,like gears or converter.