Preheat oven to 350F. Butter four small loaf pans or a 9 x 5".
With a standup mixer, cream the butter and sugar together, add the eggs one at a time beating well after each.
Whisk the dry ingredients together and add to the butter mixture. Mix well. Add the bananas, sour cream, and vanilla. Mix well. Remove the bowl from the mixer and add in the chocolate chips, stirring to combine. Pour into prepared pans.
Bake 40-50 min. if making the small loaves or 60 min. using the larger loaf pan. Cool for 10 min. then turn out onto a rack to finish cooling.