I used to be a rabid addict of that game then I beat it and "caught the all" anyway if you need help just ask me (I know pretty much every hidden item in the game).
Here's my team
Mewtwo-most powerful one in the game(psychic, recover, body slam, substitute)
Hp-405!!
At-310
Df-260
Sd-342
Sp-400!!!!
Gengar-A must have (equip him with sleep, poison, and draining attacks)
Articuno-give him flying and ice attacks(blizzard)
Zapdos-give him flying and powerful electric attacks(Thunder)
Dragonite-Extemely powerful(give him ice water and normal attacks)
Gyarados-give him water and normal (hyper beam)