If you were going to get 4, I'd make it Secret Wonders, Great Encounters, Stormfront, and Legends Awakened. As others have said, you'll get all of your staple trainers such as Roseanne's/Bebe's/Rare Candy/Night Maintenance/POTION( just kidding) out of SW and GE as well as staple support such as Claydol. A lot of the Pokemon you're going to want to base decks around come from Legends Awakened and Stormfront, although these sets will also round you out with a bevy of other useful trainers such as Cynthia's Feelings, TM-TS2, Pokedrawer, Luxury Ball, etc.. SF also has the highest number of money-fetching cards, with 3 shiny super rares, the reprinted Charizard line, and then 5 level Xs.
Even though I wouldn't necessarily buy a box of MD, I have to disagree with the statement that you it's a subpar set. Before LA and SF hit the scene, it was the best of the block. Three out of the four level Xs you can pull are playable and valuable (the odd one out being Porygon Z lv. X), and you also get Call energy, Empoleon, Infernape, Torterra, Bronzong, Chatot, the Eeveelutions, Cresselia, Darkrai, etc..