Give Vixen her Mutahuman mimcking powers, then we have something to talk about.
If Vixen is allowed to mimic the Hulk's abilities this could move heavily into the JLA favor. It would be even more interesting fight if Vixen can mimic the abilitis of the other JLA member. You think fighting the Hulk is hard, try to fighting a Hulk-Powered Vixen with a canary scream and super-streaching powers.
If not allowed, Hulk win with very minor damage . See the JLA vs Doomdays fights .
@arcus: Hawkgirl and Vixen get about the same beat down from Wonder Woman with both ladies showing impressive durability. If you watch the episode again, you will see that Vixen fights her while the others break the wall. Also, both women are going for the KO but Vixen has the offensive (strength, speed, claws, electrical shock, agility) and defensive (durability and heal factor) ability to win.
If her mace connects, she hits harder....but that's more properties of the mace not a show of strength from Hawkgirl. At most Hawkgirl is in the one ton range, while JLU's Vixen can do about 12 tons. If you look at the fight again in Grudge Match, you will see that Hawkgirl and Vixen did about the same when it came to getting their asses handed to them by Diana.
Also, Vixen's healing factor is signification enough that she can heal broken bones in seconds (see Wake the Dead), something Hawkgirl can't do. You should keep in mind that Vixen could shock the shit out of her with power of a electric eel or knock her out with super speed before she can take off. (Hunter's Moon)