Here's what I think:
Grass:
Venasaur
Moves:
Giga drain
Solarbeam
Leach seed
Overgrow
Item:
Amulet coin
Fire:
Chaizard
Moves:
Flamethrower
Flame burst
Overheat
Flame charge
Item:
Charcoal
Water:
Blastoise
Moves:
Hydro pump
Surf
Dive
Your choice
Item:
Mystic water
Flying:
Braviary
Moves:
Fly
Stell wing
Brave bird
Acrobatics
Item:
Sharp beak
Dragon:
Hydreigon
Moves:
Draco meteor
Dragon pulse
Dragon claw
Your choice
Item:
Your choice
Ghost:
Gengar
Moves:
Shadow ball
Shadow Claw
Curse
Your choice
Item:
N/A
I thought of power, coolness and strong guys. I would suggest that you put an EXP share on the weakest and then train it also. Hope I helped!