Honestly you really can't go wrong either way. Midget week offers the chance to see both kinds of cars which kind of makes it a better value in my opinion, but at the same time it doesn't go to either Terre Haute or Haubstadt. If you want to take in some other types of racing while you're here Eldora also runs some races either slight before midget week and during sprint week if you wish so that might also be a consideration. A grounds tour at IMS is also another nice little side trip if you haven't done it before and they only offer those on certain days.