Godzilla is an Irradiated Godzillasaurus; he is also known Gojira, King of the Monsters, Monster of Justice (in the Zone Fighter TV show), Big G, God of Destruction, and Gigantis.

Throughout his movies, he has been said to be 50-100 meters tall and weighed 20,000-60,000 tons. His powers consist of atomic breath, phenomenal strength and the ability to breathe underwater. He has fought a wide fariety of monsters, including; King Ghidorah/Mecha-King Ghidorah, Monster X/Keizer Ghidorah, Gigan, SpaceGodzilla, Destoroyah, MechaGodzilla 1, MechaGodzilla 2 (Only in Godzilla vs. MechaGodzilla 2), Kiryu, King Kong, Hedorah, Megalon, Megaguirus, Ebirah, Titanosaurus, Zilla, Orga, Gabara, Kamacuras Giant Condor, Battra, Biollante, Kamoebas, Fake Godzilla, Proto-Moguera Dororin, Neo Hedorah, Black MechaGodzilla, Super Special SpaceGodzilla High Grade Type Two, Gororin, and Hyper Mecha-King Ghidorah.

But he has some allies too, featuring: Mothra, Rodan, Anguirus, King Caesar, Jet Jaguar, Varan, Gorosaurus, Kumonga, Zone Fighter, Baragon, Manda, MechaGodzilla 2 (Only in Godzilla Island), Gigan (Only in Godzilla Island Episodes 118, 177 & 178), Moguera, Fire Rodan, Mothra Leo, Medical Jet Jaguar, and Fire Fighter Jet Jaguar.

Gamera is a Giant Turtle/Tortoise, also known as Gamera the Invincible, Friend of all children, Guardian of the Universe and Toto.

He is 60-80 meters tall and weighs 80-120 tons. He can fly at Mach 3 speeds and has Fire breath.

His foes consist of fought Gyaos, Barugon, Viras, Guiron, Jiger, Zigra, Legion, Irys, and Zedus. His allies are The Children of the World, Asagi Kusanagi and Toru.

Now let's compare

Species: I doubt that it is any contest comparing a Giant Turtle/Tortoise to a dinosaur, especially since Godzillasaurs are Carnivores. Winner: Godzilla

Alias: The aliases for the monsters are another huge scale tip. Gamera is called "Friend of all children"; no self-respecting monster would be called that. Not only is Godzilla is known as "The King of the Monsters", but "The God of Destruction"! Winner: Godzilla.

Height: Gamera is 60-80 meters tall, but Godzilla is 50-100 meters tall, and according to the English dub of the original movie, he is 400 feet tall. Winner: Godzilla

Weight Gamera has a weight 80-120 tons, roughly the same as The Statue of Ramses II, but Godzilla weighs 20,000-60,000 tons! That is almost 500 times larger!

Powers: Gamera CAN breathe fire, but Godzilla's radioactive breath is continuous, and if the actual blast doesn't kill you, the radiation will! Gamera has the capability to fly Mach 3 speeds which gives an edge since Godzilla cannot fly, he may outmanoeuvre Godzilla or run away. Winner: Draw

Major enemies: (for this category, enemies equal experience in battle). Gamera has fought nine monsters in 12 movies, most of which were one at a time. Godzilla has beaten 30 monsters in 28 movies, some were repeats! The King gets another point

Allies: (For this category, allies can help in all giant monster movie logic). Godzilla has fought alongside 18 other monsters, where Gamera has 3 allies, one of which is 'The Children of the World'.

Bonus information: Gamera's movies were first made in 1965 and the last one was made in 2006. Godzilla has movies from 1954 to 2004. That means that Godzilla was kicking tail and taking names for nine more years than Gamera. Winner: Godzilla

Godzilla wins