Pokémon Gold/Silver for sure. The QoL updates over Gen1 (RB) and 1.5 (Y) are just enough, although RBY was actually challenging at times GSC reduced the difficulty a tad. But the map is better, bunch of side quest options that aren't too grindey, good callback to Kanto. I haven't played the remakes but I'm sure they would be just as great.

I played the Brilliant Diamond one after not having played Pokémon for quite a while, played the gen3 ones on emulator a bit (Emerald in this case, quit when the difficulty was way too low until you got to the League, suddenly you actually had to work for it). Played Shield as well but didn't even really feel like a Pokémon game to me.

So yeah I'm a typical genwunner but I prefer the second gen games. Crystal was neat but I don't prefer it over Silver/Gold.