As a huge Batman fan, it pains me to place The Dark Knight at the bottom of this list, but unfortunately, the facts just work against him here. He might be a super human being, but he's on a team full of super-charged, super strong and just all around super beings, which makes him the weakest on the team - from a physical standpoint.
However, he's also the smartest and most astute member of the Justice League, which arguably makes him its greatest asset. The character is often referred to as The World's Greatest Detective and he earns that title, solving crimes and planning strategies to take down the world's enemies, all while fighting the good fight on the streets of Gotham City.
Batman may be physically outmatched by the other members of the Justice League but he stills stands beside them, shoulder-to-shoulder, looking every bit as larger-than-life as they do. He's capable of doing things that they can't, and rescuing them from some deadly situations.
Remember, this is the same Batman who went toe-to-toe with Superman and very nearly killed him. He's also the same Batman who learned a lot about trusting his friends in the battle to defeat Steppenwolf. And that can't be overlooked.