One tip I would give homeowners when looking at replacing their HVAC system is taking a whole home approach to the HVAC system. Just putting in a really nice high efficiency unit isn't necessarily gonna solve all the problems with the cost of energy. The attic installation and the ductwork are huge aspects of that, as well as windows and Doors. So take a whole home approach at trying to solve your needs.
When doing a home energy analysis, a technician will come out, go into the attic, go under the house. look at all the nooks and crannies of where air could be leaking from the house into the attic or vice versa. use thermal cameras to address Specific leakages that may not even be seen by the naked eye.