If you're STRICTLY concerned with SPEED here, I would say your best bet is to walk to the Boardwalk and hop in a cab to the Magic Kingdom. That's bound to be faster than waiting to get picked up in a bus at 9:30 at night and then getting taken from resort to resort picking people up before finally making it to the Magic Kingdom.

Also, just make sure you're parked at the TTC and not the Epcot lot because I don't think you'll be able to get back to Epcot via monorail after 11pm when MK closes.