Such a timely topic. I just recently had my entire cedar house exterior painted and it's new addition interior with Sherwin Williams paint. First off, if your a Consumer Reports follower, they absolutely HATE Sherwin Williams paint, giving it the lowest mark on their list along with its very high price.
http://www.consumerreports.org/cro/home-garden/home-improvement/paints-stains/exterior-paint/interior-and-exterior-sub/ratings-interior/index.htm
I've painted the entire interior of my 2 story house and I like Behr paint by far as the best. It generally is rated near the top of CR, but that is not why I started using it. The biggest advantage to this paint is that is is truely a "one coat" paint if the conditions are right. It seems to be thicker also and less splatter. The contractor painted the addition used SW paint and I had to repeatedly ask that numerous rooms be repainted because I could visible see where the coverage was thin. SW paint is the contractors and professions friend and I think they get good discounts there as opposed to Lowes or Home Depot. The top three paints over the past years according to CR are from Home Depot, Lowes, and Walmart. You pay a premium at SW, which is why you have those coupons. As far as the exterior goes, it has only been a year so we will see. Hopefully is will be better then the reports show. I think SW paint, especially the exterior oil based stains where very good at one time, but the switch to latex hurt them.