I'd have to say Maverick, Millennium Force, or Magnum.
Other than Spongebob at MOA, I've never been on a ride with a drop like Maverick's. That beyond vertical drop is a new sensation.
As for Millennium Force, that's the second tallest coaster I've been on, and the massive size of the drop does it for me.
Lastly, I don't know what it is about Magnum, but despite being a little shorter, it still has a great drop.