What new world type would you most like to have in Minecraft?

I have 2 ideas for new world types in Minecraft:

Sphere, a minecraft world that is not flat as always, but spherical like real planets.

Ringworld, Ringworlds like those in Halo mur, with the difference that this Ringworld does not orbit any planets and there's a Sunlike thing in the middle of it.

Which of these two ideas for new Minecraftworld types do you like better?

I'm more for Kugel, but the Ringwelten would also be varied, in itself I would find new worlds well in an update.