Feel free to use whatever apples you prefer. Honey Crisp apples are sweet and crispy, so they are typically the ones I choose. You can also interchange the blackberries for another berry, like blueberry or raspberry. I used an 8x8 baking dish, which gave me a thicker filling and topping, but you can also use a 9x9 baking dish or 9x13, which will spread the filling and topping out a little bit thinner.