Personally, mine is joint first between Sandshrew (the cutest), Espurr (most relatable), and Gastrodon.
After those, in no particular order, I like Turtwig (best starter, fight me), the Roggenrola line (little rock guys), the Litwick line (candles and lamps with nefarious intentions), and Metagross (cool robot thing).
Kyogre is the best legendary in my opinion
Listen, friend, I was an adult before Pokémon was even a thing. Your Pokeymans are irrelevant to me, child. Irrelevant.
So why do I recognise most of gen 1 and a handful of others besides?!
TL;DR: Psyduck