As much as I love the other worlds in the game, I had to go with Peculia. I love it's randomness, and the world perfects it.

As much as I love Karkaton, nothing holds a candle to Greenhorne in my opinion. It's a perfect inroduction to the game, genuinely feels progressive unlike most areas in the game, and is overall brilliant in my opinion. Not gonna lie, I wish Neksdor and Fey were a lot more structurally similar to Greenhorne.

Oh, and the Greenhorne-related music tracks, especially the battle and map themes, are amazing.

I agree with @Bluebatstar the Scolipede . They put little thought into Realm of the Fey.