If I remember my expanded universe lore properly, Luke had the ability and potential to be the most powerful Jedi that ever lived. Whether that potential was ever reached (I unfortunately lost track of it in my late 20's) I have no idea. So if that's taken into account, I'd go with Luke, personally. Now whether he would get to the point where he kills Yoda..? No, not in his character. But potentially beat in a duel a la Vader in Jedi? Yes, definitely.*
Hopefully we get to see all that potential in Ep VIII..!
Yoda would look cooler doing it BUT Luke will be the clear Winner. I'm not all that clear on the Star Wars story but IIRC Luke is something of the culmination of all those who have come before him. He is the most Jedi of Jedi, a little light and a little dark and all that jazz.