Chamber. Gross motor skill quickly deteriorate and it is just one more thing to do when you need to be concentrating on something else.
I am waiting on my plastic to get here. I carry at home, all of the time, in my CBST. It is fully loaded with one in the pipe. I am quite confident that it will not go off unless I put my finger on the trigger and also depress the grip safety (XDm 3.8" 9mm).