For me a good friend is that one to always is there for you, in despite if that person is your best friend or maybe just one more of them be a best friend doesn't depends about how much you love that person, because don't care how much we love a friend, if he or she is a bad influence isn't a good friend, for example if that person is indifferent to our feelings or doesn't care about us, we don't say to that person is a good friend, actually that person as a friend is a failure.
Maybe we can have many common friends, but the really good friends aren't a lot.