Generations 1-5. I have wonderful memories with each. Starting with Gen 6, I found the art style unbearable, and even if the stories / gameplay were perfect (they weren’t), I found them too divergent from “core” to overcome.

Areceus was nice because I didn’t go into it as a mainline entry; it was like playing Stadium for the first time.

I’d really like Nintendo to release Emerald, HGSS, Platinum, and BW/BW2 on Switch, as I’d happily pay. My gut tells me they don’t so as to avoid cannibalizing the new titles, but I feel like most buyers are only really engaged in one or the other.