Here are my thoughts on the rivals:
- I found Blue decently challenging since he picked very powerful and rare mons for his team, some of the best in Gen 1: Rhydon, Exeggutor, Alakazam, etc. Problem is, the AI and movepools suck...I still find him a good rival but not the best. He got better characterization on later games, when he isn't your rival anymore. Trace is pretty bland imo, and taking the role of the antagonistic Blue in a remake of RBY is not doing him any favors. He even has the same champion battle theme, which doesn't fit him AT ALL.
- Silver is...hilariously easy to beat even on his final matches despite all his talk about being strong and invencible. Nevertheless, he shows a very notable development after he gets beaten by Lance, starting questioning his flawed ideology and becoming a better trainer, which is among my favs. It gets even better in HGSS, where it's finally addresses he stole his starter and got a nice resolution out of it. Also, by fully confirming his family ties to Giovanni.
- Agreed with May/Brendan being forgetabble, these guys suck and left a dirty mark on friendly rivals. They even gave up on their journey wtf? Wally should be the main rival, having more humble origins and becoming an outstanding trainer, yet the game barely focuses on him...
- Barry is my favorite rival, unless we count N, like the tier list below does. He mixes well being your reliable friend from childhood, and also being a bit of an impatient prick. I remember he gets so cocky when he finds out the art of "just avoid all hits, attack and win lol" which translated to Staravia double teaming, and that fails. Yet, despite his lack of patience, he has Heracross and Munchlax, two of the hardest mons to find in Sinnoh. He gets beaten by Jupiter and realizes he needs to get serious and heklps you later on.
- I like Bianca a bit better than Cheren because I found her journey more relatable and interesting, but Cheren is also a pretty good character; both representing the Truth and Ideals motif of the game. Hugh has his own journey at chasing down Team Plasma, I think you get to team up more than you get to fight him, which is a nice change of pace.
- Do I really need to say why gen 6 rivals bad? Calem/Serena are marginally better, but their character and interactions are so barebones I couldn't care less, unlike....
- Hau, his easy going nature becomes a problem later on in the game when he fails to protect Lillie and realizes he needs to get serious, which Gladion called him out in Akala Island. While Gladion gets screwed by his lack of trust and communication, which Hau is good at. I wouldn't say he's a jerk rival since he respects your strength when you first met him.
- On gen 8 we got Nice Mean and In between rival dynamic. Hop was pretty good: being your childhood friend having dreams of following his bro's steps only to get a massive reality check courtesy of Bede, which really shows on his team building. He always showed interest in Sonia's work and the desir to help Pokémon, so I liked that he wants to be professor instead.
Unlike Gladion, Bede was a JERK, but like Silver, not a very challenging one. He has an interesting backstory in his trainer card and a deep loyalty to Rose, but it's like never brought up despite how potentionally good it could have been in the story, and disappears from most of the game. I like his eventual change to Fairy Gym, being more fabulously stylish and slighty more open to you despite still being a showoff.
Marnie was there. Despite being more present than Bede, she (and Team Yell as a whole) felt even more disconnected to the plot. I know she is the middle ground between Hop's friendliness and Bede's aggresiveness, but I wasn't sure what to think of her or if she really changed at all during this journey (she didn't want to be the Dark Gym Leader but she ends up with the title with little fanfare and she doesn't even appear in the postgame story), so I found her boring. Maybe if she had a more Tsunder-ish dynamic, or if she were more openly cold but not a jerk, I would've liked her better. Also, I'm lowkey salty she was selected as the best SwSh character in a poll in Japan, but at least that means this mini rant completely counts as an "unpopular opinion".
The two IoA rivals, Klara and Avery, were ok, with both being haughty yet insecure trainers that try to one up you and hilariously fail at it. I personally like Klara a bit better since she tries so hard to look sweet, not even bothering to hide her venom shortly after. Also, these two guys are the first trainers to fight you with you being at disadvantage, it surprises me it took 8 generations and a dlc for the bad guy to actually cheat, and it's not even a main villain that does it.
I remember I did a tier list a few weeks before: