>>471192201. Paul
2. Gary
3. Gladion
The other three are shit.
Ritchie's battle was ruined by Team Rocket's meddling. This isn't "Charizard jobs to a Blaziken", this is straight-up Ash doesn't get to compete.
Trip was a pathetic excuse for a rival character. If not for that first battle with Pikachu losing to a fresh level 5 starter, no one would remember him. B/W was way too unfocused when it came to Ash's rivals, and none of them belong in the same conversation as Gary and Paul.
The Alain rivalry was terrible storytelling. Ash did not deserve to win the Kalos league because his team was terrible, I will grant you, but the entire arc of Ash learning to control Greninja's new form is simply worthless because it doesn't amount to anything. Ash doesn't achieve anything significant with it. When Ash had to get Chimchar to control its blaze, the entire thing was rewarded with a final win against Paul, tying the Sinnoh story up perfectly. Ash vs Alain ends in the same spot where it began.