I love Yoda and his wise, sage-like words. I love the spiritual element he added to Star Wrs and for me Yoda is one of the characters that really elevated the trilogy to something special. I would like to actually meet Yoda and be taught by him.
However, we don't know Yoda's origins and the development he went through to get to that point. It might be that he had a tough life and learned the ways of the ofrce, it might be that he was born that way. We don't know. Maybe the fact that we don't know is one of the reasons we like him.
But with Luke, we see his development. We see his rise from naive farmboy to Jedi, and we can assume that he will go on to be as wise as Yoda, but taller. Seeing as I am ignoring the prequels, Midichlorians are of no concern to me, and I personally do not believe the force is genetic. Some are more predisposed to it than others, but it is available to everyone if they are willing to cast off the shackles of human (or alien) thought and rise to a new level. Han was not willing to make this leap, but Luke was. As a result, we can all relate to Luke, and he can be a role model to us all. We see Luke choose to better himself, resist the quick and easy way to the dark side, and ultimately make good and walk into the sunset to grow even further.
So I guess I vote for Luke.