I’ll start.
I feel like picrel manages to be an incredibly memorable route in spite of its short length. It’s got an entrance to Dark Cave, a berry tree, a few cut trees for meaningful shortcuts, and a singular trainer that gives berries in crystal. On top of that this is also a place you’ll visit often; aside from the fact that the player is likely to revisit dark cave twice, once after flash and again after rock smash (and maybe again after surf if you want a good grinding spot), the player also returns here to deliver Kenya’s mail to the sleepy guy, and is likely to pass through here when giving the red scale to Mr Pokémon. Overall I like it a lot, definitely sticks in my mind and makes the most of what little it has.