From my experience, button-head aluminum screws (on, say, a top deck) work great. The heads don't strip easily or anthing, and they are very lightweight and attractive.

Countersunk aluminum screws, on the other hand, are utter junk for these purposes. There is something about the way a CS screw is made or shaped that makes the heads much weaker! When I tried countersunk al. screws with countersunk washers on one of my topdecks, it was a nightmare...I couldn't tork down on the screws at all without misshaping the heads at least a little.

Lately, all my cars have had the standard-issue steel stuff on the bottom (with some countersunk aluminum in low stress areas such as servo mounts or battery backstops), and pretty much all button-head aluminum on the top. Sometimes people look at me like I'm crazy, but button head aluminum screws honestly work very well!