"Best" is a function of what primary purpose you want the headers to serve. Getting maximum overall HP from a drag engine versus getting the most low-to-mid RPM torque from your street engine, for example, will probably not come from the same header.
If by "the best" you mean longest lasting then the Stovebolts win hands down. Tom Langdon's cast iron headers are priced cheaper than Clifford's tubes - go figure. And if you choose to have the Stovebolt's ceramic coated inside and out they should last longer than any of us!
On a street engine running low-to-mid RPMs I recommend the Stovebolts. You'll probably get more HP and torque from your engine by using well designed tube headers but the Stovebolts will flow plenty well enough, and as I stated before, will last
much longer than anything else made for these engines. If you're planning on drag racing then I'd stay away from the cast iron headers and move to the tube headers.
As far as the tube headers go I currently run a set of Dynomax truck headers on my 1966 half ton with a 292. I also have a set of "Doug Thorley" headers of the same pattern (they're basically the exact same header) and I have a set of the Clifford "Shorty" style headers. Of the three the Clifford is, by far, the best quality tube header. The flanges are thicker and they are heavier than the 36-inch Dynomax and Thorley headers. I have never seen or held the Hedman's so I can't speak for them. Others seem to like them. Hope this helps you out.
-magic mike-
