I feel I need to start this out by sharing my belief that baseball in not actually a sport*
I would pick Jackie Robinson's first game in the major leagues.
There's history, and then there's history. To be in that crowd, to hear, see and feel the good and the bad would just be amazing.
*Baseball does not pass the lawn chair test. Before any play started, if you had all players sit down in lawn chairs, and during the course of the play, most could remain seated in the lawn chairs and the play not be effected, then it is not a sport. You can sub in grilling a hotdog if you would like.