Though I chose Litten, I actually didn't use my starter this game for the first time ever. Instead I used dusk form Lycanroc which was kind of like a starter since you get it through mystery gift.
I chose Rowlet! I was all aboard the Popplio train for Sun/Moon, but Decidueye almost made me reconsider. I'm glad I got the chance to try him out in a whole new game!
Popplio! Popplio is my favorite out of the three so for my first playthrough i choose him. When i play another run I usually choose another starter though, in my current moon run I have litten. But I have yet to reset UM because of the darn ultra wormhole legendaries
I chose Litten, it reminded me of the cats I used to have. One had a name with ?sun? in it the other had ?moon? so it seemed fitting to go with the cat starter
I chose Popplio because I think incinroar fits Hao (I think that's the rivals name name? I always forget it). I ended up ditching it because I played through Sun/moon a few times and was tired of using the starters. I think my starter for US was Kanto Raichu my boyfriend gave me from Pok?mon Blue (it was lv 4).... and if I remember right, I think I used Noibat for UM.
Litten for me. I usually choose the Fire starters in Pok?mon games. Froakie was the exception in X/Y, and I chose Froakie before Ash-Greninja was even a thing