Jason GracevsPercy Jackson

Percy Jackson If the fight wasn't interrupted, Percy would win.

Percy Jackson When they fought in Mark of Athena, Percy won, even though they were far from water.
Even if they are equals, Jason has been training his whole life, while Percy has only been training for the summers of 4-5 years.
Percy's feats are greater too. Jason became praetor of New Rome and defeated Krios, but Percy defeated the Minotaur and all three Gorgons, sailed through the Sea of Monsters, held the sky, found his way in the Labyrinth, fought Zeus, survived in Tartarus, defeated Ares in a sword fight, etc.

Percy Jackson Percy is stronger, faster, more durable, and a better combatant. Her has also tanked lightning attacks from both Jason and Thalia grace.