Whiscash
The pose, the presence, the derpy face! The bearer of unspeakable and unfathomable knowledge, it's Whiscash! Never used one before but god would I love to, I do love its entire evolutionary line since Barboach is pretty funky. Shame it's overshadowed by basically every Water/Ground type ever (especially Swampert).
Gyarados
It looks much better in the anime and early generations than it does now to be honest, 3D was not kind to Gyarados in my opinion! It feels like the toughest of the Water types available in Kanto and raising a weak Magikarp you bought from a vendor into a gigantic sea serpent who goes on a rampage and requires the strongest of trainers to command seems awesome to me.
Golisopod &
Araquanid
Alola had supremely good Water/Bug types in its arsenal and I adored them both, although I only really used Araquanid for the most part. I do love my bubbly spooder with the really overpowered ability and solid enough moves (plus those defenses, gorgeous) and it definitely trivialises the Fire trial that comes up after you catch a Dewpider! Golisopod I haven't used, but Guzma's ace was really funky to see in battle and after spamming First Impression with Sirfetch'd I think I'd enjoy using it on the targeted user of the move. They're really cool.
Empoleon
I like Sinnoh, and I like metal Pingu a lot too. I used it recently in Platinum and it was pretty good! It has a wicked design (as does Piplup and Prinplup) and it learnt some pretty cool moves even if they weren't super good (like Metal Claw and Peck). Anime gave it a good showing, I know a lot of folks want Ash to have one but I personally do not (I just don't see it) but Barry using it was cool!
Sobble
It is perfection, enough said. I will continue though - this crybaby is the cutest starter Pokemon of all time (Rowlet comes in close at second place) and I am so very disappointed in its evolution design. Inteleon looks so frail and thin! And human-like! Where did the crybaby theme go? I preferred some fanart suggestions of its evolutions myself. But still, Sobble is great!