JLI wins, for me.
Warvengers: Weapon H, Captain Marvel, Captain Britain, Sif, Bucky, Deadpool, Venom, Black Widow.
JLI: Power Girl, Captain Atom, Wally Flash, Rocket Red, Elongated Man, Animal Man, Metamorpho and.... someone?
So for simplicity's sake, PG will fight Weapon H, and Carol will fight Atom. Neither will one shot the other, unless we're using real high end showings.
Then that leaves Wally to mop everyone else up. Maybe Metamorpho and Animal Man can help out with trickier guys (Venom). But overall I'd give it to DC, based on numbers.