MK: 7DMT or Peter Pan(might do PP at Rope Drop if you are early people to see the queue which is neat) - these two rides have long lines all day, then any of the three mountains you are into(Space, Splash, Big Thunder) - don't know if you are aware, but after you use your 1st three that you can make ahead, you can go onto the app and try for a fourth from what is left for the day, then a fifth after that one, etc. This can help get some of the less popular rides for later in the day. After the mountains, Haunted Mansion, Pirates, and Buzz would be next in popularity. If you are Rope Drop people, then you can do several rides w/o much of a line, make FP for 10:30-1:30, and then try for more as the day goes on. If you have two days there, and are not RD people, you can split it up, and do 7DMT and 2 mountains one day, and then PP, a mountain, and one more the next day. Sidenote -If you would like to eat in the Beast's castle(Be Our Guest restaurant) it is very cool, with the three different rooms to check out, but try to get reservations now if you don't have them already. Brft and lunch are considered Counter Service(even though your food is brought to table while you get drinks and silverware), but you still need an ADR. Dinner is table service, with meeting the Beast, but very hard to get in.
Epcot: This is tiered, so you can only choose one of the big attractions, then 2 smaller ones. So either TT, Soarin, or new Frozen ride in Norway(remake of Maelstrom). Frozen is the most popular, so get FP for that, and then do TT and Soarin if there at RD. If you have two days there, then FP Frozen one day and Soarin the other. TT does have single rider, and with bigger cars, you might ride together anyway. Frozen is over in World Showcase, so might want to FP it for afternoon if you want to do Future World in the a.m. Most of the Tier 2 rides don't usually need FP(Nemo, Turtle Talk, Spaceship Earth, etc.) You might pick Mission Space if you do that one and one other.
HS: This is also Tiered, so you can pick Rock n Roller Coaster or Toy Story Mania(two most popular in this tier), again you can pick one and go to other first thing, and RnRC has single rider if just one of you is into it. Tier 2 most pick Star Tours and Tower of Terror. Fantasmic night show is in Tier 1, and you can try for it as a 4th later if you'd like. Star Wars has meet and greets if you are into that, and they are good to get done early in the day. There are several shows, so you can check out showtimes to cooridinate your day to see the ones you want.
Animal Kingdom - new Pandora land is opening this week, and will be popular. You can FP one of the two rides - one is Navi River Journey, a slow raft ride with things to view, and the other is Flight of Passage, where you sit on a Banshee(animal), and ride it as you are immersed in a 3D movie on the screen(described as a cross between Soarin and Star Tours) - depends on your tastes of which you FP and which you jump in line for. Otherwise there is the Safari and Expedition Everest(also has single rider) and then Dino coaster and Kali River Rapids next. There is also a FP for Rivers of Light new show at night, or you can get a dining package for reserved seating at Tiffins or Tusker House - it is a small stadium unlike Fantasmic, so good to have one of these to not have to wait long in line to get seats.