I love writing for Steven Stone (or, at least, my own twisted headcanon's version of him). In my own mind's eye, he is a gentleman in every sense of the word, yet doesn't really know how to deal with emotions--others' or his own. Because of this, I can always go deep into the emotions when I'm writing him because I'm not just analyzing them for the sake of the audience--he's analyzing them because he just doesn't really get it. He also plays well off of the other characters I throw him along with. Brendan and May are his emotional mentors while he's their voice of reason, and the camraderie between the three of them seems genuine any way I write it.
Also, this isn't so much a character as a cast, but I can't get enough of the dynamic between the Hoenn PCs and their parents. Professor Birch is the classic "awesome dad who gets a little too invested in his work", providing reasons for the PCs to be outgoing and know a lot about the Pokemon world and excuses to explore. Norman, on the other hand, is the equally classic "good guy but somewhat absent dad who's still proud" archetype, giving a strong motivation in the form of "make Dad proud and even surpass him!", not to mention all the opportunities for drama. Plus, I've said it before and I'll say it again: the world needs more daddy!Norman.
If we're talking original characters... well, although most of them aren't posted, I have literally almost a hundred Pokemon fanfics, and each of those has at least four or five OCs, often more, so we would be here all day if I started listing. Some of my favorite archetypes, however, are the classic "powerful pacifist" and "super-sweet with a short temper" tropes. The former because it opens up all sorts of philosophical questions for me to explore--while simaltaneously making way for some good comedy!--and the latter because it can be used to highlight the seriousness of a situation--the cute innocent one just lost her head; run for the hills!
"Sleep is for the weak!"
"Everything I touch turns to angst."