>>34546362This is based on my experience on the latests playthroughs.
Kanto: The water routes to Cinnabar island if not the routes before Fuchsia City.
Johto: Ilex Forest or just after beating Whitney.
Hoenn: Route 119.
Sinnoh: Everything about Sinnoh is "that park", I seriously never attempted to replay it again, I regretted buying Platinum in fact.
Unova: the route before chargestone cave, and the cave itself, it may have pretty tiles, but caves are borin imo anyway.
Kalos: I didn't even bother replaying it and I wanted to drop the game at the fucking shitty desert.
Alola: the games here have no replayability at all, and I liked SM a lot, but yeah no way in hell I'm going through that again.