First, many different brands of paint will suffice. As I wrote in another thread, I have found Sherwin Williams to be the best, but others have just as well-founded, ifn not more-experienced opinions. What you want to avoid is cheap, discount paint. So long as it is a premium brand, you will not notice much of a difference.
Second, the preparations and application will be more imporatnt than the actual paint they use. In dusty Tucson, if they don't clean the surface before applying the new coat, then any paint will fall off. If they don't cut the edges cleanly, then any paint will look messy. If they glop on the paint quickly instead of carefully smooth it on uniformly, then any paint will look clumpy. You are not just paying for a product, but also a service, and the service can determine the quality of the end result more than the product.
Moreover, you can instruct a good painter using cheap paint to change his product and still get a good job. You can't get a bad painter with a good paint to improve his lousy painting. Check out their references and take a drive to look at other houses they have done to get the best measure of which one you want to select. Look at the cleanliness of the corners, the transitions, and the trim, as well as the uniformity of the application. That is the best way to shop.
