I think pink/cherry blossom islands are absolutely gorgeous, but I personally don’t love pink so much that I’d want my entire island to be themed around it, so I’d choose to have an autumn island!
Autumn has always been the prettiest season to me irl, and autumn in-game is super pretty as well imo, so I think an autumn-themed island would be beautiful! Might look a little odd during the other 3 seasons, though haha.
I adore the pumpkin aesthetic for autumn, so I’d have a bunch of Spooky items everywhere, especially Spooky Towers, Spooky Lantern Sets and Spooky Scarecrows! The Tree’s Bounty items would also be used an insane amount, along with the Mush items (Mush Lamps would be everywhere), the yellow and red leaf piles, the Leaf Campfire, Maple-Leaf Pond Stone etc!!
Deirdre, Poppy, Fauna, Beau, Lopez, Pashmina, Pecan, Maple, Bea, Sally, Teddy, Molly etc would be great villagers to have as well! So many beautiful autumn-themed villager lineups I could make!