They both are/were very important to Nintendo, and to the game industry as a whole. It really depends how you look at it.
More important to the rise of Nintendo? Undoubtedly Gunpei Yokoi.
But, more important to the continued quality of Nintendo? The reason it still has so many fans after all of these years?
http://en.wikipedia.org/wiki/List_of_Nintendo_games_created_by_Shigeru_Miyamoto
Shigeru Miyamoto.