The best martial art:Jiu Jitsu

Who disagrees with that?
Lower weight can win heavy weight with clever use of attacking.

I would mention MuayThai too,using knee and elbow striking hard.
But MuayThai may not effect well because you must train it hard to boost your muscle before use it.

Jiu Jitsu is just doing right move and you mustn't have to using strength more than stretch and brain.
Take the opponent to the ground and choke him.