Avalon. Avalon was far and away my favorite world. The storyline was absolutely brilliant, the NPCs were funny, the crafting items were the best compared to level we've ever had, and the bosses were, with the exception of the Jabberwock, of reasonable difficulty for the level. Though I hated the Jabberwock fight, I loved the shoutout to Lewis Carroll's Jabberwocky. All in all a truly amazing world.
My favorite world is probably... Dragonspyre, because it's beautiful, in a dark way. Or Mooshu because I love Japan. Or Krokotopia because Egypt is the coolest. Or Wysteria because it's lovely there. Or Marleybone because Britain is the best. Grizzleheim is pretty. I love that Celestia is underwater. And the orange and browns of Zafaria are actually quite gorgeous. Wizard City is bustling and popular. I really love all the worlds. I guess, no favorite... Sorry to waste your time.