I always mount my HD-2s the same side up, various saws have various amounts of spitback (or not), and it is almost always on the bottom. If the top 3/4 of the filter stays clear, the pleated filter will give you more than enough air for your saw, the pleats provide multiple times the surface area of a non pleated filter.
The AM filter are often so jammed up that I think you often don't get full use of the pleats, hence the slower times.
I don't think the AM filters any better than HD-2, but they do seal differently, and some saws seem to prefer one over the other (they are not all the same). If you carefully install your HD-2s, I have never had a problem with fines.