I put one in my house last year. Been thru all this.
1) Figure out how much furnace and AC you need. AC measured by
SEER, Furnace measured by efficency. I bought an 80% furnace and a 14 SEER.
If you want tax rebates, you have to buy really high efficency stuff. Costs a bunch more, and it will take several years to get that money back in terms of energy use. Be careful not to over-buy.
2) Brands: I bought
American Standard. It's made in Texas by the same company that makes Trane. Goodman is cheap shit, York is not as good as it was a few years back. Rheem and Ruud are the same company, both are OK. Rheem is made in Arkansas. Carrier is mostly for commercial property now, residential Carrier is very expensive.
3) Make sure you hire somebody who knows what they're doing on the install. On the AC, I recommend spending a little extra for a variable speed blower motor. I also recommend avoiding heat pumps.
You'll hear a lot of different and conflicting advice. Pick a company that you trust, ask for references if you're not sure.