I usually hate all my least favorites equally but by generation
Gen 1: Charizard, Beedrill,Goldeen and Rattata
Gen 2: Unown,Delibird,Yanma,
Gen 3: Ludicolo, Nosepass, Cacturn.
Gen 4: Cherrim, Tangrowth, Infernape.
Gen 5: Amoongus, Boofalant, Zekrom,
Gen 6: Hawlucha, Dedenne, Bunnelby.