About five years ago I first found this site while trying to research replacing my furnace and adding A/C. In a "new" home and faced with wanting to add A/C to a new furnace and coil (not chosen by us), I had a different set of questions and concerns which would have been moot if starting from scratch.
I just wanted to thank the dedicated pros on this site for their advice in the midst of my persistent and perhaps annoying questions. It really was appreciated.
I started with 5 contractors and came down to 2 pretty quickly (including the one whom I hired before) using many of the suggested questions and activities (like doing one's own Man-J calc first) to weed out the pretenders. The ARI check was something new, and it actually revealed a potential issue or two in the proposed systems. As a result I have a system that for the last week has worked quite well thus far - keeping us cool and more importantly, dry. Hopefully it will remain enjoyable and trouble-free for a long time to come.
If I didn't already have such a young furnace and coil, I would have certainly explored the duel-fuel systems. The flexibility and efficiency intrigues me. Unfortunately, I'm not made of $$$ and have several other expensive projects in the near future even though this home is intended to be ours for another 20 years or more.
I've found some of the threads truly interesting (like radiant barriers on heat gain, ducting, coil/condenser sizing, and yes - the ethics one). The halls of fame and shame are eye-opening.
If I've offended anyone along the way this time with my straightforward demeanor or opinions, offense or insult wasn't my intent. For those that took the time to respond with detailed explanations, I am thankful and better off for it.