What is the best HVAC equipment?
This is a subjective answer at best. Like buying a car, all equipment has the same basic components, and many are made by the same OEM manufacturers.
Some manufacturers limit purchasing to their dealers only. This is a very stupid idea. They are increasing the cost of business with this rule. In some cases they claim superiority, but in reality are inferior to the cheapest equipment built. The difference is in the installer and the expressed warrantee. If the very best installation company uses non-experienced sub-contractors to install equipment, then the job will not usually be satisfactory. Trained professionals are needed from the start to the finish. Supervised workers can be used, but the man in charge on the job, needs to be qualified. I have supervised many tradesmen that are qualified, but not capable of running a job. When they attempt to run a job, it gets screwed up. Once again this is when an experienced construction supervisor will stop problems before they happen. Commercial jobs require completion bonds and blueprints. This adds to the job, but if the cost to redo is higher then your purse can afford, spend the extra and require completion bonds.
Use a lawyer to write the contract in your favor.