I generally stick with the same team until the post-game (unless I find any Shinies along the way), then I swap in my "signature team."
I've been having a lot of trouble choosing only six Pokémon for that signature team though. Dunsparce, Wartortle, and Mothim are static, but I shuffle between Alolan Sandslash, Porygon2, Shedinja, Glaceon, Flareon, Froslass, and Lickitung for the other three. I want to settle on six (especially for trainer cards and art), but it's so hard! One minute I think I've got it, then I start doubting...
Over the past couple years, in previous-generation games, I've been hunting to fill my post-game teams with full-odds Shinies. Too bad I transferred over most of my past-gen. Shinies before I decided to do this... ><