Logical question. Assuming you have proper ventilation from the eaves, Just insulate between the attic joists. If you insulate between the attic floor joists, you are not required to insulate the attic rafters. Don't skimp! Attics take more insulation than exterior walls. Most of the home's energy (cold or hot) escapes through the roof. Check your local codes and go an extra step. You'll be happy with the outcome.