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This is in terms of plot relevance/implementation of the Champion role.
>Geeta and Alder
I think they're some of the most well-implemented of the Champion roles because beyond just being the "strongest" of the region, they have a clear hand of involvement with the league as a whole (or part of it). The league in Unova serves as a sort of defensive force against outside threats as well as being gym leaders, which Alder takes on as the leader of them, and Geeta is the perfect boss of sorts to the corporate nature of Paldea's league. In addition, both of them are actually known about by their gym leaders/E4 and have actual character dynamics with them.
>Leon, Blue, Red, Nemona
None of them have the all encompassing "leader of the league" role the previous two did, but they all lean more onto the battle prodigy side of it as characters. Leon as a sports celebrity in-universe makes sense for a character role a Champion would have, and the latter 3 are all talented battlers but never sticks around for the actual beaurocratic duties of being one, which makes sense. They're all the shounen ideal of a champion.
>Wallace, Kukui
They both have roles within the region that lends itself well to the Champion role (Wallace for being a lorekeeper and coming from a line of them and Kukui for being a strong Professor who wants to establish a league) but either doesn't really have much beyond that, or doesn't actually stick around as a Champion. On a side note, Wallace being second fiddle to Steven and knowing that makes him more interesting to me.
>Lance, Iris
It makes sense for them to be powerful trainers within the region as that's their main goal/area of focus but there's not much there beyond that
>Cynthia, Steven, Diantha
I honestly think the first two are overrated and have the same problems Diantha does, in which they really have no business being Champions because there's nothing that solidly establishes them as such beyond just being one. Boring characters.