MK: I'd always thought the Peoplemover was the most peaceful ride I've ever been on....but I'd sleeping in that ball pit under the Space Mountain walkway. I always wanted to go down there as a kid. Probably be drawn to the Haunted Mansion too, as that howling wolf at night just sets the Disney tone for me every trip. Tomorrowland has that ridiculous peacefulness to it, though.
Epcot: I'm hanging out all night in the World Showcase, of course. I'm actually not much of a fan of France, but Epcot's france is nice. That would be of course after I raided the Fish & Chips cart in UK and had to roll on over to France. Then I'm headed to Spaceship Earth for the night to sleep under the drop off under the stars at the end.
AK: I would say something involving Everest since it's my favorite attraction there by far, but I have this weird phobia about large/deserted/abandoned structures/animatronics...and though we aren't talking about that scenario here, being alone near that Yeti activates my weird phobia thing, so I'm staying on the other side of the park from Yeti. I'm not a huge AK fan, so I'm probably just going to place it safe and spend the night in Rainforest Cafe.
DHS: Oh it's a tough one. Do you jam to Aerosmith all night or sleep under the AT-AT? Oh, who am I kidding? I'm definitely headed to the AT-AT.