Are you talking about a new purchase, or a selection from your existing lenses? If existing, take the one with the largest aperture. Without further probing, my first instinct would be to go with the 300. Oh, wait -- daytime? Probably the 400, depending upon where you are in the bleachers.
Having done a fair amount of stadium work professionally, my personal preference is to use a shorter lens, and get as close to the action as possible.
Having done a fair amount of stadium work professionally, my personal preference is to use a shorter lens, and get as close to the action as possible.