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I usually try to go with:

Waluigi: Very fast, helps for stealing the ball or hitting people who are about to take a shot. Also can wall yourself off for the megastrike, no more "cheap" in my opinion than surrounding yourself in a fart cloud or slamming the ground to knock people away first.

Hammer Bros - really only using him for his skill shot, he's too slow for much else.

Birdo - Good long range shot and moderately quick.

Dry Bones - Fast enough to stop the opponents from shooting, decent skill shot but not great.
 
Game Balance

Wow, just looking at the diverse team configurations people have chosen, it looks like they did a good job with game balance.
 
another pretty high pressure team i once used against a friend is going with

1 dry bones (in defensive position)
2 birdos
1 donkey kong

result: you can shot from every position to score goals with birdos and donkey kong.. which makes defense really hard for the enemy with charged balls and all 4 chars happen to have a great defense attack (donkey kong sliding for intercepting balls in enemy half)
after a quite leveled 3:2 game or so with equal stats i totally murdered my opponent with this team with more than 20 shots on goal opposed to perhaps 2-3
 
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