While they may be similar in appearance, furnaces can perform very differently inside. When comparing furnaces, the differences mainly come down to efficiency, followed by the motor type and stages of heating.
If you live in the northern half of the US, Energy Star recommends furnaces that deliver 95% AFUE or higher. In colder climates especially, 90% AFUE furnaces can deliver significant energy savings.
An 80% AFUE furnace can be a sensible option, especially if you live in an area with more moderate winters or you’re not planning on staying in your home for much longer.