I notice that when people ask questions, generally they receive replies asking more questions.

It was suggested to me to get 3 bids and then come back and report to you what I found.

However, it seems to me that when I do so, you will want to know this and that about my house, where I live, etc.

Instead, could you give me some workable list of questions about my situation that you would need answered in order to make some suggestions ?

I'll give you some info to start, and you can tell me what else you want to know:

House built in 1979
2 Furnaces - same models
2 AC units - one 2 ton, one 2.5 ton
All 4 units are the original article - 26 years old
I live in Atlanta, GA
The house is 2 stories, with the upper level about half as big as the lower.
One set of ducts goes to only 1/2 of the lower level.
The other set of ducts goes to the other half of the lower level and the entire upstairs.
The house is not tremendously well insulated.
It is on a slab.
It has vaulted ceilings.

In addition, it likes long walks on the beach, cozying up by the fireplace, reading, and traveling.

This way, I will have much more of a clue about what may be appropriate for my house before the sales guys visit.