Hmm. Well, the cop out answer is "whichever one I'm currently playing in!" I really do think I give a different answer every time I'm asked this question, but for today? Today I'm really feeling both of the Marleybone worlds!
In Wizard101 I've spent a ton of time running around Regent's Square exploring, and I always liked roaming the rooftops. I like the rides on the Balloon Ships with Mr. Personality. I totally love chasing down Meowiarty, and I'm intrigued by his entanglement with Malistaire. I like the night time sky and the funky bobbies. . . . It's kind of funny because I fully understand that Marleybone is the most hated Wizard101 world there is, but strangely I really like it!
And in both worlds of both games I just really like the steampunk vibe--that ALONE would escalate them to my favorite worlds. Steampunk is awesome.
How about you? What are your favorite worlds and why?