Stock ones.
Port the welds out of the openings where they bolt up to the heads. Stock headers are good up to about 280 HP. A guy on here that goes by the name Micheal Yount has a mildly built 5.0 in a Volvo, and went from stock headers to Motorsport 1 5/8" shorties I believe, and he lost 2HP and didn't gain a thing for TQ.
Buy a good H or X pipe, and a good cat back, and while its yanked apart, remove the stock headers and port them inside there,.... you'll see the welds I am talking about.