Don't know much about Mongul, but I've seen scans showing him to be stronger than Superman. He'd probably beat Thing in drag-out brawl.
Aquaman seems to be DC's weaklink, though I know his strength levels are portrayed anywhere between Class 10-100. Then you've got to take into the upgrades he may or may not still have....
If Doom's has full use of his magic, I'd pick Team Marvel. Give him prep and technological resource, and they pull it off with flying colors, I'd say.
If it's classic Doom, I think Team DC would take it.
Gladiator (confident)
Thing
Silver Surfer
Dr. Doom
vs.
Post-Crisis Darkseid
Aquaman
Mongul
John Stewart Green Lantern
Team DC
Darkseid is at least on level higher than anybody in this battle.
He would wreck Surfer, even the current one.
Mongul can take Glads and if he has the power rings even easier.
No matter how good Doom is he can't take on a straight fight a GL.
Aquaman would beat Thing.
He retains his strength out of water and he is way faster than the thing and a better fighter.Plus he has the waterhand and telepathy.