I'm gonna do just for Rejuvenation:
Hardest:
Angie (Who thought that would be a good idea a move that hits 2 targets with 20% freeze chance?)
Florin/Flora (In V10 they were even harder because of Ludicolo Surf + Cradily and if you are against Florin, nobody outspeeds his Sceptile and Flora's team is tanky as hell with the rain and field nulyfing most of her weaknesses).
Souta: (Still didn't played against him in the current release, but his field is broken and that Skarmory tailwind lead makes his team a pain).
Easiest:
Valarie (Ppl says that she used to be a demon, but now her team is slow, and a Grass/Electric with good speed take her team down with ease).
Ryland (Snow Warning Vanilluxe literally ends him if it wasn't for the Excadrill and Torterra with Crest. But anything that changes weathee and a fast or bulky super effective attacker takes him down easily).