Riper is better: use heavily spotted or black bananas - sweeter, moister loaf. Yellow bananas make it bland and dry.
Do not over-mix: stop as soon as the flour disappears; a thick, slightly lumpy batter bakes tender, not tough.
Toss the chocolate in flour before folding it in so it stays suspended instead of sinking.
Chopped bar chocolate gives melty pockets; chocolate chips work too, and dark, milk or a mix all suit banana.
Read the toothpick carefully: melting chocolate can look like raw batter - aim between the pieces and look for moist crumbs.
Cool fully before slicing for clean, moist slices.