It can be both in terms of aesthetics and lore. For example, Wallace and Milotic, at least for me, stand out because when it was released, Milotic could only be obtained by evolving Feebas, increasing its beauty. So it would mean that Wallace caught that really ugly fish, invested in its beauty, and obtained his Milotic, and as far as I remember, there's no hint on how to obtain a Milotic in the entire game (Emerald).
Cynthia also has a cool synergy with Garchomp, but more because of opposites. You imagine that a beautiful woman like Cynthia would use a more refined Pokémon, and she releases a terrestrial shark dragon with spines all over its body.
I think the one that stands out the least is Lance, due to having three Dragonites, which seems more like a joke than anything else, since none of them stand out.
by InuMatte