I like Ula'ula the most, so far has had the most interesting locations like the beach with black volcanic sand, the abandoned mall for that one trial and the desecrated Po Town which was part of the game I liked. Reminds me of some actual subdivisions I've seen in real life in not so great parts of town around here. Observatory is pretty neat too. Also can't forget about that awesome throwback to Nugget Bridge! All around most fun and interesting island to me.
Ula'ula is my favorite island, has my favorite Pokémon from Alola, the island is just so unique and has so many places to play. It give so many areas and has a lot of story behind them. I very much enjoyed this part of the game and continue to play mainly in this area.
Ula'ula! I love the Malie Garden and the more traditional housing in Malie City. Not to leave out Acerola, she is adorable. And old Nemu... He is so awkward and aloof that he makes me cringe every time I see him, but knowing what I know from the postgame, he is fairly cool now. (MINIOR!!! AND VULPIX!!!)
I'd say my favorite is Ula'ula as it was the largest and had the most stuff to do in it. I really liked the atmosphere of many locations like Po Town and Malie Garden.
Ula'ula Island!~ Because it is very enormous there are many different attractions like the abandoned mall, Malie City and Po Town, also the Pokémon you can encountery exclusively in the areas.
I quite liked Akala island. I really liked the trial captains and the Thrifty Megamart. OMG THE THRIFTY MEGAMART! It was amazing ahhhh. I loved the deals!
Even though I love every island, I love Poni Island the most! The nature, its small size and the powerful Pokémon are only a few things that I love about it. It's an easy spot to train my Pokémon (apart from the Pokémon League), especially the lower leveled ones. The Battle Tree is my second home, and it's the island where I met one of my favourite Pokémon Trainers! Can you guess who? Did you also notice how beautiful Sea Folk Village's theme is, especially at night?