Wow!
What a decision, well becides kicking myself because it's not gun season and I don't have my gun with me,
I would wait for the bigger buck.
The main reason why is because as you say he was on the trail of the doe. So odds are he will continue to come my way. Even the fact that the younger smaller buck spooked out would be a good thing cuz this brute will probably come make more rubs and scrapes to further mark his territory and show his dominance.