MK - we hop on the train as soon as you get through the gates, catch the first one before it departs and it takes you right to Big Thunder & Splash mountains before anyone walking can get there. You can ride either one at least 3 times without having to wait more than 3-4 minutes. Generally people flock to Tomorrowland first for Buzz or Space Mountain, so Frontierland is fairly empty for the first 30-45 minutes.
Epcot - usually Test Track but like Alice Sr. said, we'll be going to Soarin' first thing next time.
MGM - The Great Movie Ride
AK - Kilimanjaro Safaris, although I'm not a big fan of Animal Kingdom and I didn't go there at all the last time I was there.