So /vp/, in your personal opinions, what Pokémon game or generation of games had the best trainer AI?

The newer generation definitely has a better diversity in AI between trainer classes/Gym Leaders/Elite Four/etc, but I want to hear what you guys thing is necessarily the greatest.

By greatest, that is also a matter of opinion, so most challenging, easiest, etc, could be by any reasoning, I just wanna hear other peoples opinions.