I carry several guns, depending on where I am going and what I am wearing. The gun I have on me most of the time is a Glock 21. Why? Glock dependability and 14 rounds of .45 ACP. (Memphis is not a safe town!) However, I also carry a couple of S&W .357s, (2.5" and 3"), and I have just bought a 638 Airweight, which will get quite a bit of concealed carry. When on the road and need an all purpose, do everything gun, it's my 4" 57.
So even though I have a whole bunch of S&W revolvers, and like shooting them the best, I voted Glock because that is the one that gets carried the most.
If I had to (regarding your first question) I could use a SA revolver, however, those are my fun guns. If I needed a fast second shot, I could just do better with a DA. Also, I feel safer with the trigger pull of DA guns. A cocked SA revolver doesn't take a whole lot to set it off! In a shoot/don't shoot situation I just like that extra insurance that's afforded you with a DA.