I know it's a question that everyone would like the correct answer to, but thousands of opinions does not make a correct one. I will start out.
Headers are a waste of money on a street driven car. expensive, noisy tinny sound , heat in engine bay, leaks, don't last long..bla-bla-bla
I use stock high performance cast iron manifolds. 2 1/2" exhaust pipe, 3" does not provide any benefit. H pipe--X pipe.. I use the X as it looks higher tech.
Mufflers--no performance gains to speak of. I use Flowmasters as they are long time best known name. Gotta have 3" tailpipe___Naahh, not better, just louder. The factory, on all levels of performance , use smaller tailpipe diameter than the exhaust pipes. Got to be some reason, so I use 2 1/4" tailpipe.
If there is any responces, I bet they are quite different than what I think ! LOL............................MO