Vixen is one of my favorite DC super-heroines. She's got a neat original characterization and powerset, like Black Canary, and isn't a 'girl version' of anyone.
(Even if she appeared sixteen years after Animal Man, who has pretty much the same powers.)
When the Detroit League first launched, with the amazing Martian Manhunter as their big gun (so often given less to do on a team with Wonder Woman and Superman), and the dynamic and awesome Vixen and Steel characters, I was in love with that era. (Although I was not so much a fan of Vibe or Gypsy...) Also, Aquaman and Zatanna got some decent exposure, two more characters that tended to get sidelined in a 'classic' League lineup with characters like 'the Trinity' or Flash or Green Lantern.
But, yeah, Vixen, all the way. One of my favorite DC heroes, because her powers are just all over the place, and yet easily defined and limited. While she sometimes gets some crazy feats, like 'proportional beetle strength' or 'the speed of 100 gazelle' or something silly, even with 'only' cheetah-speed and falcon flight and shark swimming and electric eel touch and blue whale strength, she's just got ridiculous versatility. Need someone to go fight alongside Aquaman at the bottom of the ocean? She can do that. Need someone who can fly? She can do that. Need any of hundreds of incredible sensory abilities, such as bloodhound tracking, or the ability to sense direction, or create a sonar chirp? She can do that. Need someone who can pistol-shrimp-punch someone so fast and hard that there's a sonic boom and the air catches on fire around her fist? She can do that.
Need someone who can wrap up people in spider-webbing? She can do that too, as long as Marvel's lawyers aren't looking.