It's a hard pick for me, so I'll just name what is probably my top 4, Cutiefly, Lurantis, Mareanie, Sandygast
Cutiefly - does it need explaining?
Luranits - It's Totem was a pain that I spent 2 hours fighting, possible a bit longer (I refused to run off an train I just kept restrategizing because it made me stubborn) and my only thought the entire time was "damn your gorgeous"
Mareanie - Saw it and immedietly was like "I can't have you on my team, I already have a water type... but playthrough two, you're gonna be my angry lady.
Sandygast - I avoided most pokemon announcements before the game came out because I wanted to be as clueless as possible running into new pokemon. And out of all the pokemon I didn't know about that I ran into in game, never before have I so quickly seen a pokemon for the first time, and immeditely say "You are my new favorite" because like damn, sentient sand?! Got me sold! I named her Sandsa Stark in case anyone wanted to know. We're still happily a team.