No prep. Who wins.
The Avengers:
Cap.America
Cap.Marvel
Quasar
She Hulk
Vision
Scarlet Witch
Iron Man
vs
The JLA:
Batman
Superman
Green Lantern
Wonder Woman
Manhunter
Flash
Aquaman
Captain Marvel and Superman stalemate each other for most of the battle.
Supes might win in the end, but is heavily drained.
Same with Batman and Captain America.
I give the edge to Cap.
Quasar fights Kyle and takes him down either through experience or draining and manipulating the rings's power (If Pulsar [Photon] can I don't see why Quasar can't)
She-Hulk fights and wins over Wonder Woman (Shulkie's gotten stronger, but I think WW might still be stronger and has the edge in fighting experience and training) but with Iron man helping wa to much for WW in the end.
MM probable takes out Vision after a tough fight.
Flash looses to the Witch
Aquaman looses to Iron Man assuming its on land. (IIRC, Aquaman MIGHT have some super-strength, but on land Iron Man is atleast as strong if not stronger and can fly, shoot lasers, etc.)
Left:
MM, and Supes vs. Quasar, Cap, Iron Man, and the Witch
Witch and Cap could go down rather easily due to telepathy. Quasar takes out MM quickly and fights Supe. Discounting Supes' factory to pull a power out of thin air or to auto win, Supes could be weak enough for Quasar to drain enough for it to matter. After a long fight I put it toward the Avengers. As far as I know, most of the times Cap. Marvel and Supes fight Supes tends to win, but is always barely standing by the end.
left standing:
Iron man and Quasar maybe Wanda are left vs Superman
Going with the Avengers for the long and hard fought win