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Well, you could get Chimchar as your starter, since there's not much Fire Pokemon in the game. He'll be good for Fire and Fighting attacks later on.

Then, you go get Luxray, which is the Pokemon I know that can attack with Electric and Dark attacks like Thunder and Crunch.

For water, I'll say Floatzel It's because it's a Water Pokemon and has a very high stats in Speed, which is good. It can perform any water and ice attacks that could be useful later in the game.

You'll need a flying Pokemon, so the best choices are Honchkrow or Togekiss. Honchkrow is a Dark and Flying type, which you'll need for the League, and has the moves, especially Psychic. Togekiss can fly and have normal attacks, but you can teach it anything like Fire, Water, or any elemental power.

Garchomp and Roserade are great for your team as well.

I'd go with Chimchar because out of all three i think it's the strongest when fully evolved and it is fire/fighting so that can be really benficial during the game....I think garchomp and roserade are good for ur team...i would also put in a gardevoir which is a strong psychic type...staraptor is a strong flying type which u will need during the game as well and lastly i would put a jolteon in there because it has great speed and attack and it's moveset is pretty good