The question is mostly what my least favorite gen is in terms of Pokémon 
Probably gen 5 (BW era). (Using the search function that works a lot better on the new forum) I came across this older post of mine for my top 6 favorite Pokémon per gen (from Januari 2021 - some probably have changed slightly by now):
If I had to put the generations in order from favorite to least favorite, it’s probably: 3, 1, 2, 4, 7, 6, 8, 5.
So in conclusion: Joltik
Greetz,
Quuador