First, anyone who says 1200$ headers are junk, you should run from.
Most of us mortals use mid level headers and deal with small issues.
Get the best you can afford, but don't think that you need to get top of the line.
There are very small power and sound differences between them.
Heres a list based on my opinion and experience with them and based off of what ppl i know have said based on real world usage.
Along with some of the differences in the headers.
Never buy mild steel headers. Always get stainless
Thickest flanges and smoothest collectors aswell as y pipe merge.
There are other tricks manufactures use to make their headers better or performs differently like, stepped primary tubes, tri y primary's that is merging of cylinders that fire at same time of very close together.
1 7/8 or 1 3/4" primary's
2.5 or 3" collectors
Collector spikes, they smooth the flow of exhaust in the collector reducing turbulance.
Ceramic coating, inside out out.
Various thickness of the primary tube walls and type of stainless used.
There are other more subtle differences, but they exceed a daily driven vehicles needs.
Best to worst.
High end, absolute best fitment.
Kooks
Stainless works
American racing
Doug thorley
Mid level, basicly all the same, slight figment issues with each manufacture.
Texas speed
Speed engineering
LPP
Cal-speed
Pacesetter
******
Cheap but effective, and ****** fitment, most the time requiring a BFH (big fracking hammer) and a torch to get them to fit aswell as thin flanges, cheap materials, crap welds, etc.
Obx
Any other eBay crap
Anything mild steel
