Interestingly, I never realized Tubular was supposed to be the hard one. I thought it was the forest one full of Bullet Bills. Also, I love the first Special Zone stage. It's so colorful and impossibly high.
The one with special berries is nice, too. It's evening, and those sumo guys bring lightning down to the cool earth... And that secret cloud.
Lastly, I like the overworld itself--especially after a few minutes.