Strongest - Jun? (Jun was strong enough to battle Ogre who beat Heihachi and was praised by Kazuya himself but Yoshimitsu has an unknown power with the full potential of his sword)

Most Useful - Lee (highly talented, rich, can build and upgrade robots and also has an idea about commanding people as one of most important Yggdrasil member)

Weakest - Julia (Not completely sure however she has no superpowers wasn't there during Yggdrasil vs G Corp war and she also got caught by G Corp in Tekken 6)

Useless - Tie (I don't want to include Julia second time and as for King and Shaheen both did the same amount during the war they basically only defeated some troops and Jack robots)

Nice!

Strongest, Jun, as she is able to suppress the Devil Gene

The most useful is a toss up between Lee and Yoshimitsu, Lee for his tech and intelligence and being a valuable ally and friend. He and Lars work together so well. Yoshimitsu as he saved and helped a lot of people (Dr Bosconovitch, Eddy, Xiaoyu, Bryan [Even though he turned on him], and Lidia)

Weakest is Julia Chang

The most useless is probably King because even though he helped in the fight against Kazuya, he got involved in the conflict way too late