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
Probably Jigglypuff. It can learn all the attacks and evolves right away and was always fun to down air into down B combo on smash bros 64.