Bloomington's been around since the 1920s (I'm thinking 1929??)

The easy answer is IMS hands down, even though I know that answer violates the spirit of the question.

The old Indiana bullrings (Kokomo, Paragon, Bloomington, Lawrenceburg, Haubstadt) have all seen more or less the same cast of great characters throughout their existence; if you pick one, you've basically got to pick them all. If you consider the Fairgrounds, Terre Haute, Salem and Winchester, you're adding a handful of USAC/AAA names that didn't frequent the Indiana quarter miles. Outside of Indiana, you've got to consider Eldora, Manzanita, Ascot and certainly Knoxville. But the guys that ran those places (excluding Eldora) weren't seen in Indiana all that frequently.

That's a long way of saying that I don't think there's one track that can lay claim to that title.