Hi Chris. My choice for the best training game is the Montebello scenario in the files of the Yahoo group. It is small and tightly balanced. We play 2 or 3 games per evening, about an hour each. It might take 90 minutes or so while learning the rules. It also is light on the terrain. A lot of BBB scenarios involve lots of hills, towns, streams, etc.
Bull Run is good too but takes more like 2 hours to play. You had some input to that scenario design.