Until SV I might've said Bulbasaur, but now it's Sprigatito. It's adorable, the whole evo line is nicely designed, and Meowscarada is one of the best final starter evos I've ever used for battling. I always picked starters based on which one I thought was cutest at the time, here's mine each gen.
Oshawott! It’s been my favorite starter since 2011. When I was a kid I slept with a stuffed Oshawott pillow and I had an artist at a local bookstore make a really cute sketch of one for me that I still have framed.
Bulbasaur was my first favorite Pokemon back in the days of Red and Blue. It may not be my number one favorite anymore, but it (and Venusaur) still holds a special place in my heart.