Best brand of paint to use for exterior door?

I need to paint a solid wood exterior door. Only the bottom 1/3 of the door shows signs of needing painting, probably because it is unprotected from lots of sunlight and rain. This door was installed about 20 yrs ago. What is the best brand of paint to use ? Should I apply 1 or 2 coats ?Best brand of paint to use for exterior door?
If the paint is comming off of the bottom I would recommend lightly sanding the area where the paint has been damaged-nothig serious just a little roughing it up. Then prime the door once and paint it once. If it's a dark color get your primer tinted close to your desired color or a gray always works great. Primer I would use is the 1-2-3 Primer by Zinsser-they have it at Lowe's and other home improvement stores. As for paint I would get an exterior latex 100% acryllic, satin or semigloss paint. If you go to Home Depot get Behr and if you got to Lowe's get Valspar.Best brand of paint to use for exterior door?
I used Sears paint and another high priced brand name, and the Sears paint held up while the other didn't. I would use it again. I would do 2 coats, but may need cleaning and stripping first.
I think I just read something about Behr paint having the number one rating according to Consumer Reports. I would apply 2 coats of paint, one being primer (underneath the paint). That should do it.