A large older home that was retrofitted with central air, you should consider the option of pulling it out completely and going with mini splits. It's more expensive to install but will provide a lot of flexibility in how to cool the home.
A newer house, designed with central air, pick a seer rating that can fit your budget. Talk to at least a couple of different hvac people who can understand thermal load.
If you're planting trees that will provide shade in 5 years, that will change the thermal load and your ac may not run enough to remove humidity. Same thing if you need to remove trees or other features.
Like any job there's people who plug numbers in to a table and get an output and there's people who understand how that table works, it's deficiencies and how to compensate for that. If you can find that second type of HVAC tech they would be ideal to advise you.