Hmm... good one. Though I'd side with the Tranformers. Though you didn't really say WHICH Transformers, I'll accume the Autobots and the Decepticons teamed up to fight the Gundam team. The Transformers can morph into cars, jets, tanks, and planes. They can do anything that the Gundam robots can... and the Gundam pilots are human. It will be one hell of a battle, but the Transformers will have the victory in their favor.
100 Roman Gladiators vs. 70 Civil War Confederates