I feel like the question is misleading. Do you mean the most insane, so the craziest coaster, or the scariest? Because a crazy ride does not need to freak out GP upon sight, a scary ride has to by definition.
BTW the most insane/craziest one is Tornado at Bakken. And it’s likely not even close.
To the public, I'd say there are a few top contenders: - Eejanaika. This looks bonkers off-ride and I'm sure it's just as crazy on-ride. - Kingda Ka. Tallest coaster in the world (currently), of course it's going to scare the general public! - The Smiler. Whilst the record-breaking number of inversions is probably a good factor of what would make people intimidated by this ride, I still feel like the accident that occurred in 2015 is the true reason why guests might feel a bit uneasy going on this. - Any of the 200ft+ RMCs could make this list. I can imagine that giant wooden structures with metal track throwing you in all directions is a big scare for the general public.
To enthusiasts: -Eejanaika. Yeah, I think this one probably looks bonkers to everyone. -Intimidator 305. The main thing I hear people talking about in regards to this coaster is how often they've greyed/blacked out after the first drop. I'd definitely feel intimidated before going on this one. -As mentioned above, Tornado. It looks absolutely insane, but that wouldn't stop me wanting to ride it in 'boost mode'.