JL and Avengers stands NO CHANCE. Even an immature Total Mimicry user could win. They could literally Mimic the Gods of their verses and unalive them instantly

An Immature Total Mimicry user would let their guard down thanks to their childish personality, but this a poll featuring a total mimicry user with the JL and Avengers powers and abilities alone vs the two iconic groups

I'd say JL and Avengers. A skilled Total Mimicry user is uber, but he is still one person and we know the superheroes fight god-level beings every other day. I believe some of them have Total Mimicry too.