Which pokemon should i pick in the bigging of the game?
It really doesnt matter which one you choose. I like Squirtle just because of his overwhelming type advantages against other pokemon and his brute strength. But its your game. Also once you beat Blaine (7) you can go to the Sevii Islands. On Two Island you can learn a special move depending on which Starter you choose.
Bulbasaur=Frenzy Plant
Charmander=Blast Burn
Blastoise=Hydro Cannon
They all have 150 attack and 100 accuracy, 5 PP, and the same effect. After you use it you have to wait a turn to recharge.