I've used Sherwin Williams for years and they're good products.
I switched to Dupont for the convenience I have with that jobber.
I honestly don't think you're going to see a quality difference in
any of the major brands.
I'd opt to go with what the painter likes, if he's more comfortable with
one line you'll probably get better results with that line.
And, you won't have to worry that he'll blame the brand you used if
he screws up.