The OBX are the cheapest but are kind of junk. The Doug Thorley are the best and you can sometimes pick some up on a group buy for around 4 or 5 hundred.
Like Elton said, the work required to install them isn't worth it unless they are the last restrictive piece on the engine. A MAF calibrator will help you get the gains you are looking for after the header install.
If you have a crack, best to go with Doug Thorley instead of stock because you'll be doing the same install anyways.