I do play Pokemon albeit not slightly competitively so I don't have much say in why a certain character would use a specific pokemon because of its attacks and stats (mostly anyway); regardless, here it goes!

First of all, one of my fav chars (per my recent app) Judge Magister Gabranth (couldn't fit the whole name in the tag hence Gabranth only).



I see him as having gone for the all the badges/defeating Elite Four as soon as possible and having a pretty physically tough (high attack/defense and bulky/hardened pokemon) team for the most part, hence all the rock/steel/ground types. Something that can raze the enemy without problems whereas not so attuned to attacks of the non-physical kind.

I also see him being pretty close to his Steelix especially; such a magnificent powerful pokemon under his control, that's enough to give anyone a power kick and one knows that's something Gabranth does enjoy (whereas not as openly in the game, because of the Empire and whatnot).

(I'll edit it as I go and manage to do so before the deadline; still trying to come up with more characters)