Mr Paint will only use Glidden. Steve likes Sherwin Williams, and I like Benjamin Moore. Quality counts, but I suspect you will get good results with any of them. As far as the extra cost between brand X and Behr at Home Depot, you will probably get what you pay for in any paint, and what you pay for is the solids content which improves hiding and blending.
Wish I could be more specific, but the last thing we want to do around here is start "Paint Wars" Mike. A very messy affair.