The best systems in my opinion are in order Mitsubishi is probably the most reliable, Quite and efficient the drawback is heat pump only, Trane XV18 or XV20 pretty much Mitsubishi technology since Mitsubishi technology and Trane USA combined and formed the new company METUS but are pricy I...
Anytime I'm selling something and suspect that I'm being scammed I just say I only deal ftf at local sheriff's office and I never hear from them again go figure.
I would mostly question your home, insulation in the attic, insulation in the walls wall insulation deteriorates over time and starts compacting down and can leave over a foot of non insulated wall at the top, floor insulation if on a slab seal plate leaking air, also air infiltration seals...