Pedro, it depends on witch enigne you will use it on.

F.eks: I get the smoothest engine with the 41021 type manifold and a very good fuel economy on the Top Elite 5.
But the engines is even better with a little more snap and revs with the 41001 header that is angled in two 90 degree bends.

On my Mantra, 41001 is not so good for me, as it gets a little to snappy and i use the 41021. I usually use the 2096 pipe on both engines.

Edit: the doubble bend headers usually makes more snap and the curved ones is smoother. I have compared on OS and Nova engines. Headers that i have compared is the same length and diameter and not nessecerly OS or Nova manifolds.