So to answer the question, which one is smarter and why, I think you have to decide what does "smart" mean to you? For me, when I think of "smart" or even call it wisdom I think of Joe the mechanic that fixes my car. He works in a field that he loves, makes enough to live comfortably but not spoiled and is often happy about his life. His family is close and he has good relationships with his customers and friends. Most importantly, he isn't out chasing some unrealized dream. To me, he is one of the smartest men I know.
Therefore, I would go with Billy Graham. Graham found his calling at an early age, followed it with all of his heart and energy, used what he gained to positively influence millions of people and will leave a legacy that any of us should envy. You may not believe in what he believes in, but you have to respect that he has held true to those beliefs his whole life. And, I don't equate him to any of the flash in the pan TV evangelists who fall apart when things go wrong (and thus expose their lack of faith/belief).
Dawkins is a seeker and an academician. He found his area, certainly, and has put his heart into proving what he believes. But he continues to pursue the dream of proving himself right. Is it a valid endeavor? Certainly. But, does he have the same level of contentment with his beliefs and the same level of happiness with his knowledge? My opinion is that he doesn't, which is why I would pick Graham as the smarter or the two.