Not sure if it's my favorite but I really love Route 209 and the egg hatching route through the daycare above it. Spent a lot of time as a kid slathering honey on the tree in it and the one at the end past the daycare, trying to get a Munchlax. I eventually did and didn't learn until recently about how only certain trees are randomly chosen to spawn him at the start of the game kek
Also the OST for it is pure kino
https://www.youtube.com/watch?v=ZMOYXIG5OzQ 