Preheat oven to 350. Grease muffin tins or line 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 flour mixture into 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 muffins from the oven and allow to cool for 5 minutes before removing from tins and allowing to cool completely. Store in an air-tight container. Makes 18 muffins.