Fire red will always be my number one as it was my first game.
Otherwise it’s a hard choice between Sapphire and Heartgold. Both had great regions and lots to do.
My most played would be Diamond and it was good, but sinnoh was never my favorite region.
Shame, I have strong opinions around Discovery. Mostly because every episode is “fate of the universe” and character development arcs usually fizzle our with little actual change in the characters