If the current equipment is 25 years old then I am skeptical they are rated for 12 SEER. If that is true then installing 14 or 16 SEER equipment is not going to yield a significant energy savings.

Are you going to live in the house or flip it? The advice will be different based on what you plan to do.

Post the size of the house and location so better advice can be given. As for brand you need to determine which brands have good dealers in your area. The installation is more important then brand. But there are some brands which cater to budget equipment that would be appropriate if you are selling to make a profit.

@mike_home Thank you. House is about 5,500 in Las Vegas. Not sure about flipping or keeping. 50/50 at the moment.

Typically HVAC conditions can be a negotiation to get a cheaper price, but only if the buyer is wise enough to pay an HVAC professional to investigate it.

The way it most often goes: home inspection specify's things wrong with HVAC system. The owner of the home then hires HVAC company to check / represent them. Which is a conflict of interest for the often times (lack of a better word) foolish new home owner.

The new home owner is often times worried about money fleeing their wallet before they even have a contract on a new place to live. In a world of $10K, $30, $100K over asking price? So HVAC might be the last thing on their over heated minds.

Flipping: The most profitable way is to avoid doing much of anything. Lipstick on a pig, kind of thing. You're doing this activity to make money. You'll make less replacing the HVAC system(s).

Maybe where this makes more sense is $high dollar$ real estate. But people with that kind of money maybe they won't care. What's $25k among strangers when the list price is over a million? You know assuming there is more than one HVAC system and everything needs to be replaced for both.

But because it's in the desert maybe touring the place with a broken ac isn't too desirable at getting a motivated buyer.

The summer design temperature for Las Vegas is 106 degrees F. Your 5,500 sq. foot house has a big cooling load. Have any of the quotes provided a load calculation? If not then I suggest you keep looking for an installer. The quotes should have details of all the model numbers and a description of the work. A good installer should also provide 2-3 equipment options and pricing.

Amana, Maytag, and Lennox can be good. However most brands have a range of equipment from the low to high end. I recommend you stay away from the entry level model and target a SEER 16 rating. Pay attention to the EER rating. In your climate the EER rating is more important than SEER in my opinion. This assumes you will be paying for the electric bill.

I usually advise going with the brand that is popular in your area and has a good installer. The most recognized brands are Carrier/Bryant, Trane/American Standard, and Rheem/Rudd. In some parts of the country Goodman is popular. Where I live it is almost nonexistent.

The prices of houses are going up in most areas. It is hard to say how much of your AC investment you will get back on a resale. Normally I think it would be half.

I would be interested to know what equipment is currently installed. If it is 25 years old then that would be impressive surviving the heat in Las Vegas.

"Currently has 12 SEER units. I have heard electricity usage is amazingly different with newer units and with 14 or 16 SEER."

You heard wrong. You probably won't notice much of a difference, even with 16 SEER, over 12 SEER.