Silver Age Superman is the strongest version of Superman. Superboy Prime or Superman Prime is his equal since he is a real person who gets the power of Superman. Since SilverAge is official dead that would make Superman Prime the strongest yet he seem to can't handle ION a being that represents the full power of the Green Lateran. Then if we are going Marvel Hulk, and Thor are up their but Thanos could beat both of them. Oh and before they killed him off a character called Sentry owned the Marvel Universe.