Just like the best chocolate chip cookies use a mix of white and brown sugar, I find it best to use a mix of brown and white sugars when baking muffins, since they impact the texture and flavor or baked goods differently. In addition to sweetness, brown sugar adds a bit of moisture and caramel flavor to the muffin batter. White sugar creates a lighter crumb and a hint of crispness. For the perfect blend of moisture, structure, and flavor, use both sugars!