Be up front on what you're looking for: Cheapest price, best service, best warranty, better efficiency, etc. They run the gamut. I personally prefer a company that will be there if there are issues. Without good customer service, a new AC means nothing. Also ask if there's a cost advantage or necessity to swap out your furnace at the same time. With prices going up all the time, it pays to weigh that option if your furnace is the same age. Also, don't ask, but see if any company that comes over actually does a heat load calc on your home. Very few do, which leads to issues. The new ACs typically need bigger duct work and filtration. A company that is up front with that knows their stuff, vs. someone who comes in and spends 15 minutes quoting a like-for-like swap.