The more I read retro clones the more I want to get a copy of B/X, I've posted about it before http://3toadstools.blogspot.ca/2013/09/some-bx-love.html . Having never really played B/X, I can't say that its my favorite edition. I remember playing red box with a friend and thoroughly enjoyed it as well.
Officially the only edition of D&D that I own is 2nd Edition, and while its not entirely my favorite, it was the one that I played the most. Rather than say "this is my favorite edition of D&D" I think I will rather answer the question by saying this is my favorite clone.
I love the mechanics a lot! (its easier to figure for newbs) , I like the Old School-ness, Honestly I like everything about it. Go download a copy today - www.basicfantasy.org
I've tried out a few retro clones, and while I love a lot of things about them, I really like basic fantasy as it feels like a new game to me, not being very familiar with D&D 3+ , I quite like the ascending AC, it makes it far easier on the DM, and dealing with bigger battles etc. Everything else to me feels just like any other version of D&D.