Quoted By:
Always
>Fire
>Water
>Grass
>Electric
>Flying
>Wildcard (usually Psychic is the smartest way to go, or Ice is nice. Ground is nice to have as well)
Obviously using dual type helps, such as Water/Ground. Probably best dual type IMO. Or Fiire/Fighting
This covers Fire, Water, Electric, Grass, Ice, Fighting, Ground, Flying, Bug, Rock, Dragon, Steel, Poison. And if you have a fighting move, you're set against Dark and Normal as well. If you have a Bug move, then you're set against Psychic and Dark as well. And if you've got a Ghost/Dark move, you're set against Ghost. Consider:
Common moves
>Fighting: Brick Break (can be learned by like 300+ Pokemon)
>Bug: X-Scissor (about 100 Pokemon) or U-Turn (250ish Pokemon)
>Ghost: Shadow Ball (400+ Pokemon) or Shadow Claw (200+)
>Dark: Chances are, one of your Pokemon learns Bite/Crunch. If not, there's Thief and Payback, which can be learned by about 648 Pokemon.
Perfect perfect team:
>Swampert
Surf
Muddy Water
Earthquake
Hammer Arm/Ice Beam
>Sceptile
X-Scissor
Leaf Blade
Leaf Storm
Energy Ball/Earthquake
>Typhlosion
Shadow Claw
Flamethrower
Eruption
Brick Break
>Eelektross
Crunch
Thunderbolt
Flash Cannon
Dragon Claw
>Skarmory
Fly
Air Slash
Night Slash
Steel Wing
>Alakazam
Psychic
Shadow Ball
Energy Ball
Recover/Psybeam