I prefer the mirror polish but not only from a performance standpoint, but a maintenance point of view. The smoother the metal the more difficult it is for gunk (not the best word choice, but it really fit here lol) to build up and attach. This gunk can build up and restrict flow, so its a matter of preventative maintenance. Just remember, no matter how smooth your ports are they will eventually "gunk" up, smoother just doesn't "gunk" up as fast in my experience.
