Not worlds, I'm talking about zones, for example: Olde Town, Wizard City, or Caliburn, Avalon.
My opinion:
Favorites
The Grand Chasm Past, Dragonspyre: The Grand Chasm Past showed how beautiful Dragonspyre was before the Dragon Titan attacked. Sometimes I wonder what it would be like if we were able to clean up Dragonspyre.
Vestrilund, Wintertusk: The area always seemed to me like a quaint area of summer surrounded by the harsh winters of other Wintertusk areas. It seems very warm and green
Mirkholm Keep, Grizzleheim: Mirkholm had lots of interesting caves and other features that made it fun to explore.
Barkingham Palace, Marleybone: Barkingham was a refreshing visit to Marleybone, one of my favorite worlds, and we got to see Sherlock Holmes again!
Crown of Fire, Dragonspyre: The great battle against Malistaire, atop an active volcano. Unbelievably intriguing.
Least Favorites
Tyrian Gorge, Khrysalis: Always getting pulled into battles by those annoying millipedes.
Graveyard, Darkmoor: Too much farming...
Village of Sorrow, Mooshu: You all say Dragonspyre is depressing, yet you've literally got a 'Village of Sorrow' in Mooshu. Like, everything was dead there.
Zamunda Outskirts, Zafaria: Way too many defeat and collect quests!!! Greyhorns bring especially exhausting memories...
Atlantea, Aquila: Generally just a boring experience. The Sand Squid was so unbelievably aggravating to defeat.