Spinosaurus was THE biggest and one of the Strongest Megatherapods of all time, overpowering almost every land killer. It was a part of the Spinosauridae family. It ruled the Egyptian lands and waters, and Co-existed with Carcharodontosaurus, Bahariasaurus, Rugops and Deltadromieus. Giganotosaurus was a huge carnivorous therapod or a MEGAtherapod that ruled the lands of South America, co-existing with other therapods like Ekrixinatosaurus, Buitreraptor and Alnashetri. If T rex was the Mike Tyson and Spinosaurus was the great Khali, then the Giganotosaurus was the usain bolt of the MEGAtherapods.
Talking about skulls Spinosaurus had the longer skull but the skull of Giga was more wider. The teeth of Giga were sharp and serrated, used for cutting and slashing, where as spinosaurus’s were not that sharp and were used for gripping fish and other prey.
Spinosaurus gets the advantage when it comes to size. Spinosaurus: 20ft x 50 ft. Giganotosaurus: 18ft x 40 ft.
Spinosaurus: 7t-9t Giganotosaurus: 6t-10t
Arm Strength, Lifting Strength, Tail Strength and Neck Strength-Spino
Jaw Strength, Strike Strength, Leg Strength-Giga
Giganotosaurus being lighter was more agile on land than Spinosaurus, and Spinosaurus being faster in water.
Spinosaurus likely had a deadlier lifestile than the Giga, with large Crocodylomorphs such as Sarcosuchus wading in the waters while large therapods like Carcharodontosaurus in the lands. To surivive sometimes Spinosaurus had to fight these deadly creatures.
Giga on the other hand was the only large carnivore in its habitat. Also there werent any dangerous preys that it had to fight to stay alive. So points like size, length, height, weight, mass, claws, adabtability, locomotions, dexterity, intimidation, Arm Strength, Lifting Strength, Tail Strength and Neck Strength goes to spinosaurus while the giga only gets jaw strength, strike strength, leg strength , bite force, and stamina.
Thus in a 1v1 fight on land, Giga would win with high difficulty, and in water of course Spino with HIGH EASE.