Problem is the question.... as "best" depends on your end use and your end configuration and well as where on the HP/Torque curve you want your header to help. Unfortunately, most go for the glory of peak HP.... which is not all that it is cut up to be.
Ask what the road racing winners use? Belanger (makes power where needed), ask what the Nitrous folks use? Belanger (flows lots) Ask what is best for a custom built motor bought as a package? SVSi, HMS, TNT, Lingenfelter, etc. (as they optimize their headers for their packages). Best to bolt on and enjoy? Edelbrock (as it is CARB legal), bolt on and enjoy on a stock Viper with no carb concerns? Borla 1 1/2" long tube, bolt on with minor to big mods, Borla 1 5/8" long tubes, or Belangers. The Borlas do not have true merge collectors, so they do not get that last little HP as headers that do have merge collectors like SVSi, TnT, B&B.
Best is a relative thing, and quite frankly, there is more than one answer when it comes to parts selection.
