Hey Gail, that's a great question that deserves several responses. I agree with Steve on his reply, but I will say that I've worked with the Ace Royal line of paint quite a bit and have had that in all the rooms of my home for about 4 years now. It's great paint. I've used Martha Stewart and it's a paint that covers well and gives you many color choices, but I don't know about it's longevity. Many preferred paints are based largely by what region you're in. If I were you, I'd do like Steve and visit a pro paint store OR call a couple local paint contractors and ask them what they use/what they recommend.
Choosing a paint brand doesn't have to be too difficult, but I'd just warn you that everyone has their own opinion and I'll guarantee you that you'll never find the concrete answer that you're looking for, but good luck.