Preheat oven to 350. Grease the muffin tins or line them with paper liners. Combine sugar, oil, and eggs in a large mixing bowl. Add in bananas. In a separate bowl, combine flour, baking soda, baking powder, and salt. Slowly stir the flour mixture into the banana mixture. Add in the milk and vanilla. Stir until just combined. Fill muffin tins 2/3 full. Combine ingredients for streusel using a fork. Sprinkle the streusel over the top of each muffin. Bake for 25-27 minutes or until a toothpick inserted in the center of the muffins comes out clean. Remove the muffins from the oven and allow them to cool for 5 minutes before removing them from the tins and allowing them to cool completely. Store in an air-tight container. Makes 18 muffins.