Started from the bottom now we're here
In the attic.... which had pretty laughable insulation. Since this house was built in 1941, there isn't really a ton of insulation in the walls and what was in the attic was so smooshed that it wasn't really doing much to help keep the house warm or cool. We decided to rent a blower and top up the insulation in the attic last fall with the hopes of having lower heating/cooling bills and keeping it more comfy in the house. Home Depot will rent you a blower and it's not super difficult to use. We decided to go with the Owens Corning Atticat blow in insulation.
This stuff is really easy to blow in and we got it done in a couple of hours. We now have about 15 inches of insulation that allegedly won't settle over time sitting like a big blanket up in the attic. It's definitely a two person job because you need one person up in the attic and one person feeding the insulation into the machine that chops and blows the insulation. Definitely worth it and we have really felt a difference in how much the temperature varies in the house on really hot and really cold days.
For more info about AttiCat, you can visit the product page.