Features to look for in headers:  Mandrel bent stainless steel primary tubes; factory style emission connections; extra thick
collector domes; carb certified executive order number; 50 state legal; 3/8" thick CNC laser cut flanges; oversized exhaust
ports (accommodates cylinder head porting); and most of all, FIT FIT FIT!  Make sure you are familiar with the manufacturer and the company you are buying them from.
 
When it comes to headers, and you've probably already heard this, the Golden Rule is
YOU GET WHAT YOU PAY FOR!  Do your homework!  This is not the time to go bargain hunting.  Hot Rod Magazine
has rated headers as one of the top 10 performance parts to install on a vehicle.  Headers are used to replace the inefficient OEM
manifolds.  They have individual primary tubes that are mandrel bent for a smooth exiting of exhaust gasses from the
engine's combustion chamber; therefore the vehicle has less back pressure which means more power, better fuel economy
and longer engine life.   
 
Recently I stopped by a shop that was installing a set of headers (brought in by a customer) for a 90's GM truck.   The technician was swearing and throwing his tools around the bay; I asked him what the problem was and he replied that he had to redrill the holes in order to get the studs into the engine block and now he he couldn't get the steering mechanism back into place because it wouldn't clear the headers.   He asked if we carried that part in JBA, called his customer for the ok, and we delivered them the next day.  The technician has said he will never again install any other brand header but JBA's .  
 
Greyhound Performance has chosen to sell JBA Headers for all of the above reasons.   They can be purchased in stainless steel or with silver ceramic or titanium ceramic coating to reduce heat.