I have a philosophy here that applies to many things. When over 80 percent of the project is my labor, I won't pinch pennies on material costs.
For paint, I have settled on Dunn-Edwards. The shop in town has civilized people that give me good advice and don't have an "attitude" because I am not a pro or regular customer. I won't begin to tell you about the treatment I got from Sherwin-Williams, and we won't even talk about Home Depot. Dunn Edwards offers various quality tiers. I get the second from their top tier, which they call "Sparta-shield".
A quick note. Don't fall for "contractor grade". This doesn't mean what you think. It means "barely good enough" and is cheap so the contractor can make more money.
Tom's Home repair pages / tom@mmto.org