Good luck is right. The last time I had to install a new AC I had to call in about 4 or 5 installers before I got the right answer. Most of them just wanted to replace what was there with a similar unit or "upsize" it based on their gut. The AC was put in by a large national home builder. I'm sure they bought 1,000's of them and didn't size it to my specific floor configuration or site orientation. In addition, I had extensively air sealed and added insulation, so I was sure they couldn't just go based on their gut (most of these guys are just salesman BTW).
My recommendation, if you have the time, is to run some rough estimates in regards to your HVAC needs. It's been years, but I was able to find some trial software that allowed me to do this. This arms you with a little intelligence on the topic.
Then, I would invite several companies to bid on a system for you. I used Angie's List and other sites to narrow the list down. You will start to see the hacks who are out trying to just make a sale from the true pro's who want to provide you the best comfort. Out of all of the persons I had out on my job, only 1-2 ran the calcs through the manual J to properly size my system. The person I went with actually recommended a smaller AC (which I had already estimated). Bigger isn't usually better when it comes to HVAC.