Glad to hear you are interested in getting headers on your Mach, either one will be an awesome sound improvement.
If you can afford to do it, the long tubes will give you the best sound and performance. They are the most free flowing you can get, and this translates into big power and sound gains. If you do go with long tubes, I would get the BBK ceramic coated headers. The ceramic coating will dissipate the heat the quickest and keep their look under the hood for years to come. The only down sides to these are you must get a shorty mid pipe at the same time which increases their cost, and they have a difficult and lengthy install. If you can afford this and/or have the ability to install these, the long tubes are always the best bet.
Shorty headers will also improve power and sound, and are a more reasonable upgrade. You won't get quite the gains you will see with long tubes, but still noticeable pick ups. The big advantage of these is that they have similar overall dimensions as your factory manifolds and this makes them cheaper and easier to install.
Either mod is a nice upgrade on Machs. Keep in mind if you do pull the trigger on either of these, we offer a 6% discount to our forum members. If you have any further questions please get in touch with myself or our customer team. Good luck!
Depends what you mean define as qualifying for "best"
If you want stainless steel and to pay a lot of money - American Racing, SLP, or Kooks
If you want the power boost but realize stainless steel isn't necessary - Pacesetter, Flowtech, Mac, or BBK (I'd go Mac or Pacesetter)
If you want to lighten your wallet and free up no horsepower - get shorties
If you are planning a wild turbo build - go with custom forward facing headers
Only benefit of the expensive brands is you can get larger primaries, which only applies to a small number of combos with very radical builds.
You also need to think about the transmission. If the designs of some brands have not been changed you will have clearance issues trying to get the tranny out. Of course if that doesn't bother you then it doesn't matter.
just installed pacesetter headers in my mach last weekend. now the easiest way to install headers in our cars is to drop the k member. my headers fit perfect mounted perfect and cleared everything. also im not going to grantee anything as I haven't pulled my tranny yet but it looks like I can pull it without finagling with the headers. I would definitely recommend pacesetter again. I went with the 1 5/8 primaries as im probably going to stop building the engine at 400 rwhp and throw the bottle at it....