What is your favourite region in the Pokemon Universe to write in? Or do you come up with an entirely new non-canon region or city?
I've said this a dozen times, but I usually write in my made-up region of Voitto (which is a Finnish pun of Johto, Johto meaning "the lead" in Finnish, while Voitto means "victory"). I like being able to come up with my own folklore and culture, although much of the culture has been inherited from the other regions, seeing as how Voitto is a region full of immigrants.
That said, one of my stories does take place in Sinnoh, so I guess that's my favourite, then. I'm most familiar with Sinnoh, since I haven't played other games than Diamond much. I have the Japanese version of Crystal, but I can't play it right now because I have to study English and Japanese destroys my English skills. I don't really know why, but that's just what happens. So, yeah.