From a person that eats them rather than makes them, I prefer a crispy, firmer crust, such as french bread. I think they hold together better after dipping. I hate when the whole bread gets soggy and the roll falls apart before I can get the sandwich to my mouth.
In order to be a true Dip Sandwich, the bread used must be a type of French bread. It must be a fairly dense, crusty variety to withstand the abuse it receives from repeated dipping into the meat juices. This is why a French baguette or pistolet roll are most often used. Softer breads and rolls should not be used because they will disintegrate quickly. So the next time you make this sandwich try one of those types of breads.