1. Pikachu, because duh. 2. Greninja because of Ash-Greninja. He was released but may come back in the future. Also, Alain's Charizard used hacks. 3. Snorlax, because 6 moves. Enough said. Also, he has a great win/loss record. 4. Infernape, because of a great moveset, strong bond and incredible power. For the rest, I don't know. Charizard, Sceptile, Krookodile, Goodra, Noivern, Primeape, Muk, and many more are all viable options. The only reason Charizard isn't on the main list is because it's current moves are a bit lacking in usefulness. You can take your pick of the other Pokémon mentioned for the last 2 slots.
Pikachu because obvious reasons Greninja. Ash Greninja can do some serious damage Charizard. Charizard was one of Ash's strongest Pokémon Torterra. Grass/Ground allows it to take down electric types that could threaten Greninja and Charizard. Goodra. Although not his only Dragon Pokémon it knows rain dance that will boost Greninja's Water Shuriken. Infernape. Able to take out ice types quickly and blaze boosts its power extremely.