Definitely mixed. I love running a tanky, impenetrable team of Pokemon, only to Baton Pass it right to something with offense for days. But, if I'm not feeling particularly strategic, I'll just use my Fairy powers and mow 'em down in one hit. >:)
Offensive when going through the story for sure. I feel it tends to be easy enough without needing to worry about defenses. But there are those rare moments where things get tough (battling Elesa if you chose Oshawott as your starter) and I'm forced to go a bit more defensive!
They dislike conflict, and if they need to escape from enemies, they will roll away.
90% of the time I stick with offensive moves while playing in-game. Once and a while it makes sense to bust out a more defensive strategy, but most of the time there's no need to, so I never bother.
Any time I'm battling against someone else though, that 90/10 pretty much flips the other way. I love playing the long game and trying to out-strategize someone with statuses, stat moves, weather, etc.
Offensive is a must to get through the game quickly, but I tend to go defensive if I struggle for battles, so a bit of toxic stalling or switching around here and their. Maybe I'll even give my team buffs at the start.
Offensive is pretty much objectively the best strategy for the main games imo. The enemy AI doesn't have enough nuance to it (+ the inability to switch out most of the time) to make defensive play or competitive tactics like stalling really worth the effort. Only the occasional hard boss made me feel the need to switch things up - in the Ultra Necrozma fight I had to lead with my Zoroark with a disguise to bait out a useless Psychic and waste one of its turns, which gave me room to barely scrape together a win. But needing that kind of thing is pretty rare in Pokemon.
Offensive is really the only way to go in-game. If you have a few levels on your opponent, you can make sure everything goes down in one turn. No attacks for them, no damage for you, no defense needed.
As much as I love to use stall teams - and believe me, I have tried to train Shuckle in-game as well (note the word "tried") - it just takes way too long to get through the game.