Graham Womack of Baseball: Past and Present polled several hundred people about who the most important people in baseball history were. His results can be seen here. Some may flip and flop numbers 1 and 2, but I think either of them would be a good answer for the top spot.
Down list is where it gets more fun. I mean, both Marvin Miller and Bill James are in the top 10, and I KNOW that’ll tick some of you off.
This, by the way, is the best stuff of the offseason. Arguing about things like who the most important people in baseball are.