The purpose of the thumb safety on certain guns, 1911 for example, is to prevent hammer falling without intentionally pulling the trigger - I.e. banging the gun against the way, reholstering, .... , these guns generally have a lighter trigger pull.
I personally wouldn't carry a revolver unless I had absolutely no other choice. A malfunction with a revolver there is no way to "fix it" whithout taking off service, a semiauto gives you the chance to clear the malfunction.
I guess the bottom line is to carry the gun you feel comfortable, practice with, and trust it will go bang. Regardless of the gun, it is suggested that a handgun should be carried with a round on the chamber, and I think most of us agree with that.