It would just seem to me that a double would be the simplest to learn and operate in a highly stressful situation, but I've never been in that situation so I defer.
An interesting example I read concerns a hunter in Africa while looking for a wounded buffalo in high grass was charged and when he shouldered his double grabbed the back trigger. When his first shot failed to drop or stop the charge he kept reaching backwards with his index (trigger) finger looking for the second trigger.
His training and muscle memory had always been centered on the sequence of placing his index (trigger) finger on the front trigger then moving backwards to the back trigger but under this stress his motor skills failed him and they were not honed enough or keen enough to realize he had initially grabbed the back trigger. The PH dropped the buffalo with two shots from his double. A Westley Richards I believe.
