I dunno how I feel about the Unova rivals, which is to say I didn't really like them, mostly because they never really got expanded on as characters. They all fell into one of two categories:
1) Caricatures.
2) Satellite Characters.
The people in group 1 were Trip, Stephan, and Bianca (and then Cameron). Their whole characters were defined by one insufferable quirk. Trip was a non-abusive Paul who loved the word "boonies" and is seriously butthurt ALL THE TIME for no real reason because Alder is laid back and not a panic attack waiting to happen. Everyone got Stephan's name wrong, and that's all there is to say about him. Bianca is clumsy and knocks Ash into water every time they meet. Umm...congrats? As for Cameron, he is my most LOATHED character archetype. He is the "lolrandom" character who everyone loves for his affable stupidity, or rather, DESPITE his affable stupidity. Yet despite the fact he is incapable of breathing without help, he always succeeds at anything he does. I...just...no.
The people in group 2 were Burgundy and Georgia. Both of whom, you may notice, are the rivals of the "companion" characters Iris and Cilan. Their whole personality, their whole character, is defined by their rivalry with a protagonist. They literally revolve around the main character (Satellite Characters, ho!) and do nothing else. Cilan comes off as eccentric and a bit show-offy at times. Burgundy's sole reason for existing is to show that Cilan is so "down to earth" and not a show off with his connoisseur abilities; how could he when the only other connoisseur we see is that crazy-dame Burgundy? Georgia's characterization, likewise, revolves around her rivalry with Iris.
I'm hesitant to say I dislike their characters, but only on the grounds that there is no character for me to base such assumptions off of. They all had potential, but they all fell into ruts rather quickly.
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I'm going to have to jump on the Sinnoh rivals bandwagon, sorry to say. They were interesting characters that didn't revolve around a single forced joke and existed outside of the realm of Ash and Co.