Preheat oven to 350°F (175°C) and grease a 9×5-inch loaf pan.
Prepare the streusel by mixing flour, brown sugar, granulated sugar, cinnamon, salt, and melted and cooled butter until thick and crumbly. Set aside.
In a large bowl, whisk together flour, sugar, baking powder, baking soda, salt, and cinnamon.
In another bowl, whisk oil, melted and cooled butter, eggs, vanilla, sour cream, and buttermilk.
Add wet ingredients to dry ingredients and gently mix until just combined.
Fold in chocolate chips.
Pour batter into prepared pan and spread evenly.
Sprinkle streusel topping evenly over the batter.
Bake for 55–65 minutes, tenting with foil if needed.
Cool before slicing and serving.