New Worlds or the Old One?

One of the first things I consider when creating a story is if I want to create a whole new world, or merely use the one we have in a different way. I like both, so to me there is no right or wrong here, just a choice that will ultimately affect the rest of the story of and about that world and the characters living within it.

I tend to prefer alternative Earth stories as opposed to post-apocalyptic, though I'm not against those, either. Alternative Earth forces certain restrictions -- the continents must be at least somewhat similar to how we know them, if I want to insert magic, it has to have a stronger explanation than "that's how it is here", and any creatures need to conform to what we know has and can exist on Earth.

When making up a whole new world, of course, then, in a sense, anything goes. I enjoy the freedom to make a world how I want it to be, sometimes with disregard to physics. It's my world, I can make the scientific laws as well as the rest.

So, how do you like your fantasy worlds? Brand new to explore completely, or based on Earth, to find the differences and similarities?

Yours in wonder,
Anita Ensal