Yoda was more advanced training, Ben was the basic instruction. They each had an important role to play. If Ben had lived, I'm sure he would have taken Luke to see and train with Yoda at some point.
I still think people are missing the fact that R2-D2 was present during most of (if not all of) Luke's training by Ben and Yoda. Therefor that little droid contains the knowledge to be the greatest Jedi training master of all.