Paul vs Barry, and it's not even close. Barry admired Paul as a trainer even though he knew nothing about his true color. When they first met the contrast was already made, as one was really happy to get the free Beacon badge while the other was absolutely disgusted. It really showed that Barry takes battles very lightly and wants to shortcut everything to become the best, while Paul understands the process and takes training very seriously. At the league, the contrast was made again as Barry went into his match vs Paul as if it's the true testing ground on where he stands as a trainer and focused a lot on trying to impress Paul, while Paul merely looked at Barry as just another trainer he had to go through. The battle itself was well done, as Paul managed to cripple Barry's speedy Pokemon handily. Barry seemed to overreact to every little thing and gets too excited/flustered in all situations, while Paul was focused all the way through. It was a true display of a naive and overconfident trainer who thought he was good vs a trainer who experienced a lot and knows what it takes to be good.
The other two were trainers that they never met before the league, so there's that.