Aquaman is a great mentor; that whole 'talking to fish' thing was reconted to 'telepathically dominating sea animals to do his bidding'. He is nearly as strong as Superman, and has the advantage if the battle goes under water. The King of Atlantis also has access to an arsenal of techno-magical weapons, and an army of soldiers, scientists, and sorcerers.
He's a very misused character.
Kaldor'am (Aqualad) is a pretty cool. In the first season of Young Justice he was The Team's field leader, but in the second season it's revealed that he's on a deep-cover mission to infiltrate Black Manta's organization, under the justifications that Black Manta was Kaldor's father and that Kaldor's love (Tula/Aqualass) had died on a mission for The Team.
I agree that 'Aqualad' is probably the worst name (outside the Legion of Superheroes' Matter-Eater Boy), and he's outgrown the costume in the series finale, but he's still a pretty cool character. I would have liked to have seen more of him in Season 3, but, alas, DC Animated and/or Cartoon Network decided to not renew for a third season.