I always have a round chambered in my HD gun, and/or in the gun I am carrying. I don't want to have to rack the slide or otherwise try to charge the pistol in a self-defense situation. If there is time enough to do that, then perhaps there is time enough to look for alternatives out of the danger. If not, I don't want to be racking the slide and chance that I will induce a malfunction under stress, like not fully retracting the slide and hanging the round instead of chambering it.
On my other pistols, not being used for HD or not being carried, I do have the magazines loaded but no round chambered. If I want to look at them, clean them, or otherwise handle them, I can just drop the magazine and they are safe and clear (I always check to be sure anyway.) That way, I don't have to worry about dropping the round out of the chamber, and then reloading it...with possible bullet setback, etc. If, however, I do need a second gun, then the magazine is loaded and a round can be chambered if needed.
As others have pointed out, you can opt for either a pistol with a safety, or a pistol with either a DAO or a DA/SA action whose trigger pull is sufficiently long and hard to help preclude NDs. Otherwise, proper firearm handling should avoid any NDs...a modern firearm will not fire without the trigger being pulled.
