Yeah, the hardest Nuzlockes are Black and White 2, Ultra Sun & Moon, and I think Platinum.
Nah, Gen 1 is pretty easy because trainers will only ever have moves from their mons' level up moveset not TMs, so they'll have a bunch of garbage with even less synergy than usual.From there, I imagine older generations are toughest just because Psychic types are OP and dark types were mostly awful - so OG Red/Blue and Gold/Silver would be fairly tough, again especially if Nuzlocked.