Ask 10 different contractors and you may get 10 different answers. Personally, I install and service equipment that I can easily purchase and parts are readily available to me. I do not buy brands that make it difficult for me to get parts and make me pay dearly for. So therefore, I am also biased due to this. In terms of bang for buck, on the lower end, you can't beat Goodman equipment. They used to have a bad reputation but that was years ago. They have a 10 year heat exchanger warranty. So if the heat exchanger goes (the most expensive part and most important) within 10 years, Goodman will give you a brand new furnace, no fine print. Also remember, that the equipment is really only as good as the installer. Most people do not understand this but in the HVAC industry it is very true. Find a reputable contractor that is known for top-notch work and expect to pay a little more for him. Knowledge and skill is everything when it comes to ensuring a quality installation. The equipment used really comes down to preference and what you're looking for in terms of comfort and efficiency. If you're in a hot climate, you probably want to go with high seer ac equipment and skimp a bit on the furnace. If you're in a colder climate, the opposite may apply. A few high end brands that come to mind are Trane, Carrier, Lennox, Rheem-Rudd, to name a few.