I've just finished the main story, so here's my main team.
1. Popplio / Brionne / Primarina
I usually go with the water starter and despite the temptation of Rowlet I decided to go Popplio. Popplio was great in the early game, I barely used Brionne and it got most of its levels through EXP share and Primarina was awesome. My final moveset on it was Sparkling aria, moonblast, shadow ball
and psychic (I think). It is also holding the Primarinium Z which lets it use its really powerful personal Z move which also has an amazing animation.
2. Pikipek/ Trumbeak/Toucannon
I wasn't planning on using Pikipek for very long when I caught it, but this thing really grew on me. It has a cool design, a really solid attack stat and quite a diverse movepool. Unfortunately the one I caught didn't have skill link but it still did well for me anyway due to the amount of sand attackers in the world. Final moveset was drill peck, brick break, bullet seed and flame charge. It was holding a sharp beak as I decided I wanted more regular boosts in damage. I might change it to the flying z move when I go get that.
3. Cutiefly/ Ribombee
I had decided I was going to use cutiefly not matter how bad it was, but it ended up not being a burden at all. Ribombee outspeeds almost everything in the game and it has a pretty solid special attack stat. Also it is one of the cutest pokemon ever made which is my main motivation for picking pokemon. Moveset was bug buzz, dazzling gleam, psychic and pollen puff and it was holding the buginum z.
4. Mudbray/ Mudsdale
I didn't plan on using this one for long when I caught it either, but after only a couple of battles it had earnt itself a permenant spot on my team. This thing is a complete monster, with a super high attack stat and a fantastic ability, Mudsdale was by far my teams MVP and got me through the champion battle with no problem at all. Its moves are earthquake, heavy slam, rock tomb and superpower (although I only got super power after the champion) and it is holding the groundium z.
5. Komala
Komala has been a bit of a mixed bag. It was a bit underlevelled and so I was trying to train it up without grinding which meant it fainted a lot as I was putting it in unreasonably tough battles. However I still wanted to use it, just because I loved its design so much. It has a really solid attack stat and actually started to do quite well. The biggest downside was having slam as the best move for most of the game as slam has awful accuracy. Final moveset was slam, thrash, wood hammer and brick break. It was holding the normalium z (mostly because seeing Komala use the move was kinda funny).
6. Alolan Vulpix / Ninetales
This thing was too pretty not to use (even though it was the third fairy type on my team). It also ended up doing really well for me with a great special attack stat and solid special defence. It was the last team member I got and was hard to train as a vulpix, but once I got it into a ninetales it was a fantastic asset. Final moveset was ice beam, dazzling gleam, extrasensory and hex.
Honourable mentions go to Gumshoos and Lyanroc (day) as they were part of my team for a good period of time until they were replaced by Komala and Ninetales respectively.