Suggested by Destroyer Harry Potter has a good array of spells at his disposal but Percy Jackson has super human abilities. He can move with super speed and his durability is on a different level. Harry can throw his spells, but it will be pretty easy for Percy to dodge them all and counter attack. Harry is unfortunately a one trick pony. Percy Jackson wins.
DReager1.com 
Here’s the fight:
Harry was walking around a suspicious fort that looked like it homed a garrison of Death Eaters. Eventually, he found some. “EXPELLIARMUS!” he shouted to every single one. “STUPEFY! “SECTUMSEMPRA!” And they were all lying on the floor. But then, a teenager with eyes like his, messy black hair like his, but was slightly taller and was wearing an orange t shirt that said “camp half-blood” could this be another wizarding school that’s built for half-bloods? Harry thought. But that teenager didn’t have a wand. “Did you kill all these people?” But he didn’t wait for a reply. He lunged with amazing speed with a sword but Harry just dodged it enough to just get a shallow slice. “PROTEGO!” Harry said, and there was a shield. “Expelliarmus!” And the sword flew out of Percy’s hand, but then Percy got a pen from his pocket and transformed it into the same sword! “STUPEFY” Percy dodged it “PETRIFICUS TOTALUS” Harry yelled, but Percy dodged it easily. Harry heard a rumbling. “SECTUMSEMPRA!” Harry yelled, and it finally hit Percy. He was sprawling on the ground, but suddenly, the rumbling became louder and a huge wave of water appeared! It touched Percy and Percy was healed quickly. He then made the water into a cascade of trident, and hit Harry with every one of them. Harry was sprawling, and he knew what he had to do. “AVADA KEDAVRA!” but Percy was ready. As soon as he heard “AV…” he knew something dangerous was coming. He summoned a wall of water, and both the green light and the water were destroyed. Harry knew he was going to die, because Percy was about to stab him. Harry braced for it. But then he saw Ginny walking with another girl who had blonde hair and a dagger. That girl had the same shirt as the person who was going to kill him, and she yelled, “Ginny! Isn’t that your boyfriend with the scar?” “That’s right, Annabeth!” “PERCY!” She bellowed and the would be killer called Percy froze. “Annabeth?” “Yes, it’s me. No leave that boy alone. “Oh… sorry, I thought the guys he killed were innocent. Should’ve asked first.” “Oh seaweed-brain, you really are EXTREMELY STUPID AND IGNORANT!” “Sorry, and what’s your name?” “Harry Potter”
And the two became friends. They said their own story’s, and then introduced the girls. “This is Annabeth, and she’s really nerdy. She’s the daughter of Athena.” “Really? I have a friend like that called Hermione…” “This is Ginny, and she’s the sister of my best friend. Ron Weasley. Their family has 7 Children!” “Wow! Zeus has got some competition.” And then they strolled off.
Definitely a wholesome ending there at the end. I definitely wasn’t expecting that and thought they were just going to keep beating each other up so that was a good end twist. At the end of the day it’s always good to see the characters just getting along instead. I do think it’s hard for magic to beat pure stats though