If you really want to same some money on your heating and cooling bills, spray foam at the underside of your roof is hands down the best option. This is especially true if you have heating/cooling equipment in your attic. We did it a two years ago and it has saved us quite a bit on our heating/cooling costs. Cost was $2700 before 30% tax credit. Another benefit is that the attic becomes unvented and “semi conditioned” which drastically reduces the amount of dust and insects that come through the vents and eventually into the house.