My tweaks to a very good base recipe:
1. Cut the sugar in half since the bananas already provide much flavor and sweetness.
2. Mash (instead of slice) ripe or overripe bananas. Add 1 or 2 more for extra rich texture and flavor.
3. Greek yoghurt (instead of sour cream) works really well. This adds the necessary acidity to avoid having the alkaline taste of baking soda plus, helps to keep the muffin Moist.
4. Include a teaspoon of baking powder.