What would happen if powerful robots fought against each other? [Fiction, Games, etc]

One thing that's in my mind lately is what would happen if powerful robots fought against themselves. Like:

Metal Sonic, Exo mechs, Ultron, Mecha Godzilla, Optimus Prime, Megatron, Liberty Prime, Genos, EVA-01, Amazo, A.M., Zero and Sigma (mega men x), V1, Cyn, etc.

Who would be the best one? And taking in mind an actual battle, letting the robots have every power they need, that includes:

Transformations, Merging/fusions, Hard mode options, at their full powers (Like Metal having all chaos emeralds), everything canon, etc....

Also, the list that i made can be added for more robots if you want, so you can bring like GLaDOS if you want.