Discworld - I just love stories from Terry Pratchet and there are lots of them (40 books).

Before Disney it used to be Star Wars because it has so much potential for any kind of story. You can go super science fictiony without encountering any kind of fantasy elements. You can have a western type setting, dystopia, magic, drama, comedy, any weird combination of them all.

Earthsea by a country mile.

Roshar, in Brandon Sanderson's Cosmere books in the Stormlight Archive series. Everything from the magic system and the cultures to the animal life and the weather patterns are all really unique and totally immerse you in the world. Absolute masterclass worldbuilding.

Boring answer, but probably Middle-earth/Arda. Just such a well-crafted world with deep and interesting lore.

Runner up would be Bas-Lag from China Miéville's books. Very unique, somewhat Lovecraftian steampunk world with many weird inhabitants.

Pern. Just the quirk of it's physical environment that I don't want to give away, and the way people lived because of it felt very unique to me. It was so integral to the stories, too. You often see unusual environments in fantasy and sci-fi, but often only while setting the stage.

Possibly considered a bit basic or boring, but definitely Tolkien for me. It's a classic for a reason, and personally it is still so special to me

One of my earliest and dearest childhood memories was my dad reading the Hobbit to me when I was quite small. We later read the trilogy books as well. Loved them all. Recently read them all with my daughter, creating a whole new set of precious memories.

Cradle by Will Wight because the characters are endearing and believable and tangibly grow as people while they grow in the magic system which while we're at it is very satisfying variation on Chinese martial arts "magic" systems, the power scaling is nuts.

The world is deep and interesting and you get a lot of insight into it from other characters perspectives

It's 12 books and everything builds from everything you've read naturally. The themes speak to me, etc.

Probably Warcraft and Starcraft because I grew up playing Warcraft and Starcraft BW. It never gets old to me.

I would say Ascendance of a Bookworm is my favorite but it's not The Best world.
Disc World would be the best. Naussica from the valley of wind, and Made in Abyss had very good worlds but they lack depth.

Alagaësia, 1st high fantasy book of mine + interesting magic system

The Culture, because you could have every other world inside it.

Depends on the definition of fantasy. Star trek if its not limited to sword and sorcery. Then maybe xanth if it has to be magic. This is based on where I would want to live if I was in one because most of them are horrific or at least have all sorts of wars and conflicts and the average person does not have it so good.

The Temeraire Series by Naomi Novik is one I go back to every now and then. Historical fiction where dragons serve the purpose of air force during the Napoleonic Wars in England. I stared reading, but also quite like the audible narration.

Do videogames count as well? If so, then Hyrule - specifically the one from Breath of the Wild. There is something incredibly tranquil and peaceful about that world ... I could get lost in there for days.

Otherwise, I am Team Discworld. GNU Terry Pratchett.

Warhammer: Fantasy world. I didn't get into 40k that much, and that world, especially in End Times before killing it off for a remaster was so vivid, morbid and satirical. Having both strategy and shooter games of a refined quality helped it too.

Other than that, MythAdventures by Robert Lynn Asprin. Isn't consistent, didn't age well, but I love to reread these books from time to time. I really liked some jokes and characters here.

Truth be told right now it’s One Piece. I never watched / read when I was younger, but was aware of it in the periphery. I watched the first episode of the Netflix adaptation and immediatly decided that it might be worth checking out. 900 some odd episodes later and I’m kinda sad I’m near the end of what’s currently available. Is it dumb as shit? Yes. Is it immensely charming and at times genuinely moving? Yes. Could it use a massive trimming of the fat—oh god yes. But still I love how completely zany the world is and how unabashedly batshit crazy things get.

Maybe a little old-fashioned (the first book was written in the 60's), but I love Jack Vance's Gaean Reach setting. Thousands of worlds with each of them containing a multitude of civilizations, each of those with their own strange customs. Some of them advanced, others medieval and some of them almost completely alien.
For me it is one of the best universes when it comes to exploration and experiencing new worlds.

Flash Gordon universe.

Particularly from the 1980 space-opera of the same name Flash Gordon. This is a fun movie.

Narnia. Morality as a physical force. Accessible multiverse. Magic. Benign deity. Talking animals. Sex with talking animals.

The wizarding world. I thoroughly enjoy Harry Potter and anything related to it (the books, movies, Hogwarts Legacy game, etc).

Imagine living in a world where you can enrich your life and the things around you with magic, spells, charms…

Malazan.

Most books, including the ten book series, are by Steven Erickson. There are several other books by Ian C. Esselmont. Read them in publication order regardless of author.