This is probably not the official "correct" thing to do with the different shades of aluminum, but i tend to use regular aluminum, the use white, or dar for some panels, or flaps of small sections. This give more texture to the finish.
Polished is for getting a high gloss, and I don't use it much except on commercial aircraft, or test/experimental models.
I have not used the duraluminum
www.naplak.com/modeling ... a free site for modelers
www.scalehobby.com/forum/index.php ... a nice Modeling Forum