Superman vs Kryptonian
Batman vs Agent Zero
Wonder Woman vs Terrax
Flash vs Makkari
Green Lantern vs Iron Man
Aquaman vs Electro
Martian Manhunter vs Drax the Destroyer
Green Arrow vs Bullseye
Hawkman vs Atlas
Atom vs Interloper
Elongated Man vs Vision
Firestorm vs Scarlet Witch
Zatanna vs Clea
Captain Marvel vs Beta Ray Bill
Plastic Man vs Sandman
Blue Beetle vs Beetle
Too much. Waaayy too much. Eliminate the scrubs, and keep the heavyweights. Go from there.
You asked though so I'll give my opinion.....upon visual inspection JL because of team speed. However, the first major spellcaster to win his or her respective battle could end up causing major problems for the other team.
Superman vs Kryptonian I say toss up
Batman vs Agent Zero I say Zero
Wonder Woman vs Terrax I say Terrax because of the power cosmic and Axe
Flash vs Makkari Toss Up
Green Lantern vs Iron Man 60% to Green Lantern
Aquaman vs Electro I say Electro he is very powerful
Martian Manhunter vs Drax the Destroyer I say Drax to strong
Green Arrow vs Bullseye I say Bullseye because of his Adamantium
Hawkman vs Atlas Atlas is way to Strong
Atom vs Interloper Atom wins hard fight
Elongated Man vs Vision I say Vision
Firestorm vs Scarlet Witch I say according what I heard I say Scarlet
Zatanna vs Clea I say Clea she a very powerful witch
Captain Marvel vs Beta Ray Bill Beta Ray Bill wins 90% of the time
Plastic Man vs Sandman A toss up
Blue Beetle vs Beetle a Toss Up
Golem, it's not really all that bad a thread. And, in the big picture it's really irrelevant who in my opinion is a scrub vs what you think is a scrub. The real thing is to keep the contestants to a minimum, if possible.