DA/SA is fine if you've got a pistol with a good DA trigger. That's crucial. The difficulty of shooting the DA first shot has been vastly overblown (again, assuming you are starting with a good DA trigger. I consider the DA trigger on my Beretta Elite II to be a very good DA trigger for a stock gun, if that gives you a point of reference. I also don't find the HK USP DA trigger to be unmanageable, although others here have found fault with it -- not the best, but I can shoot accurately with it for defensive purposes).
The key to DA is a lot of dry firing on a regular basis. I enjoy that sort of practice, so it works for me. A gun owner who rarely takes his gun out of the box would probably be better served by the Para Ordnance LDA or the Glock. Personally, I really, really like Para's LDA. This is the kind of double action I've always wanted for a carry gun, and if Para can prove to me that they've overcome some of their quality control issues, I'll be waiting in line for this one.
DAO is not terrible. The revolver guys have lived with it for a long, long time and managed quite well. Again, it all comes down to the quality of the trigger and your willingness to practice with the gun.
The Glock "safe action" is not nearly as safe as it sounds. Because it's a very light "Double Action", there have been occasions where the trigger and the trigger safety have snagged on something resulting in a discharge, and of course there is no guarding against user stupidity on any gun. It's an innovative system that requires no manipulation of manual safeties under stress, but I suspect it could be made even safer.
Plastic is fine. I was skeptical at first, but it's largely proved itself to me (my USP pretty much convinced me). Supposedly it lasts longer than aluminum frames (and I have two of those as well). Steel is nice if you don't have to carry it all day, since it adds weight and usually, therefore, controlability. And of course, good steel frames are very, very durable if properly cared for.