Keep in mind, this isn't based on stats or anything, it's just based on how much I like the Pokémon.
Meanings
S: Truly great Pokémon, some of my favorites.
A: Not quite S, but excellent Pokémon that I'd happily have on my team.
B: Not my favorite by any means, but good Pokémon all around. Ones I'd have on my team.
C: Okay Pokémon that have some good traits, but also some bad ones. I'm generally mixed on these ones.
D: Not the worst, but not one I'd ever use.
E: Sorry to any Quaquaval or Inteleon fans, but I don't like these Pokémon in any form.