Reed Ricards, Tony Stark, and Dr. Doom vs Thanos...
Scenerio 1: Reed, Tony, and Doom get one sided prep. Their mission: hunt down Thanos and teach him a lesson. The arena is the entire Marvel Universe.
Scenerio 2: Reed, Tony, and Doom compete with Thanos in the Infinity Gauntlet saga to recover the Infinity Gems, knowing all he knows. Who gets them first?
Scneerio 3: Both teams get a year of prep, but only have access to their standard resources (So no finding a Cosmic Cube or something) then go to war.
Scenerio 4: Non prep battle.