If we are talking attendance, I'll say any of the thrill coasters.
Personally, I was devastated to learn Scream Machine was gone, then losing Rolling Thunder over the winter. I think if/when Batman:The Ride goes would hurt me the most.
My son (almost 9) actually yelled at a group of teens yesterday whom were smoking walking towards Kingda Ka (way before the smoking area). And, the 2 that were smoking? Dropped the cigarettes and put them out.