As far as brands go, the architects and paint subcontractors I work with in my day job all swear by Benjamin Moore when it comes to quality and coverage. That being said, BM is usually more expensive than other brands. We used it in our primary residence and love how it turned out. I have also used Sherwin Williams on many Healthcare projects where the client specifically asked for SW due to its durability in a hospital environment.
Many painters will suggest a certain brand because they get a better discount with them than other brands. All depends on the painter's relationship to the local distributor. And of course, if you found a color you like in a certain brand, the painter (or you) can always match that color in a different brand.
Hope that helps!
