-sigh-... fancasting...
Who the heck cares who plays Aquaman if the entire world, including many comics fans, percieve him as a joke with no useful abilities? How is his costume the bulk of a discussion when no amount of costume can make him look either cool or relevant standing next to Superman.
I say give Aquaman a small part, really a multi-scene cameo with character development. Let him reject joining the group at first. Too proud, too busy with his ocean, then during a crucial part of the film, say an overwater chase, suddenly, Aquaman surges from the sea, grabs the fleeing guy while he's turned to verify Superman is chasing him, Orin rips him a new one and disappears under the sea. Superman demands the body and Aquaman denies him. There, now he has a personality, and he's useful. Not a bad start, eh?