I don't think that depends on qualities. It depends on understanding, on trust, on complete one to another, on conect.
My best friends (I am lucky, I have several important persons in my life ) haven't any special qualities. They understands, support and I feel well when I am with every one of them.
But there are a lot of people with a lot of good qualities wich I don't consider to be my friends or one of my best one simply because we don't fit, because there is no connexion.