Love me some battles! My stories are generally fairly battle heavy (watch me reaching for a battle scene when I'm unsure of how to structure a one-shot, lol), and I always appreciate a great battle scene in stories that I'm reading, too. Some of my favorite fights that I've written are the Indigo League tournament battles in the middle of Salvage. It's not often I can justify going all-out with the most powerful pokémon and complex strategies, so those were a lot of fun to write. I can't really recall a least favorite as such, but oof, the battle in Chapter 13 could definitely stand to be condensed.
Trainer battles in my fic are generally pretty formal--more or less anything can happen out on the trail, technically, but usually people keep it clean and it's just pokémon going back and forth the way you see in the games and anime. And in gym battles and large tournaments, the rules are strictly enforced! But when pokémon are battling not for fun or prizes, when it's a matter of going up against the "bad guys" or breaking into a place or similar, then all bets are off, and it's not uncommon for the trainers to get caught up in the action, too.
I have a lot of thoughts wrt battle-writing tips; someday I really do intend to write up a guide to writing pokémon battles, heh. But in the interest of brevity, probably the most important thing is to understand the battle's role in the story! Battles shouldn't happen because the writer feels obligated to include them, like they "need" to show what happened in this gym battle. They should be advancing plot and/or characterization somehow. They often take up a lot of words, and when done poorly, they're frequently pretty dire, so I think it's important to really step back and ask yourself why you're writing a battle here instead of having it happen off-screen.
