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BW (and 2) cast actually had some role in the whole thing. Most Gym Leaders had some sort of purpose in the story, and if they didn't they had additional development on BW2 if you linked your BW1 data. There was also N, which you could sympathize as he kept appearing and interacting with you from beginning to end. There was also the Elite 4 interrupted by Plasma which was something completely unexpected from the whole series, for then forcing you to catch the version's legendary and face N and Ghetsis.
XY on the other hand... eh. Almost all Gym Leaders are plain and just there for the badges, Team Flare and all Lysandre's objective comes out of nowhere. Sure they were foreshadowing, but other Team Bosses went straight forward with their goals, or tried to manipulate from the shadows like Ghetsis. In the end most of the XY story comes from AZ, and that's almost at the end of the main game.
The Rivals is hard to say. I like Hugh since he had a reason for being angry at Plasma, simple and similar to Silver but works. Bianca and Cheren (Mostly Bianca) had some good development and you could see how they end on BW2. On XY they made it more diverse with a group of people (One who wants to fill the dex, other just pure casual, and other a fair rival)., but overall Shauna is the one who gets the spotlight even though you barely fight her.
Still, BW had a sequel and thus more content for expand their story, while the other games had the rehashed third version. The closer to a sequel in the series is RBY with GSC since explains Team Rocket situation and Red.
