What Type of Sand for My Sandbox?

If I were to get a chance to run a B/X sandbox game which setting would I use for a base? Understanding that I would change a bunch of stuff no matter what the source.

The first three that came to mind are:

1. Blackmoor - as a standalone - no Mystara or or Greyhawk or anything. I would go back to the beginning where Blackmoor is a village, the Castle is unexplored as is the surrounding wilderness also no Svenny, Blue Rider, etc. I like the fact that adventurers have the option of exploring the Castle/Dungeons or the wilderness.

2. The Elphand Lands from the Wilderlands. I would likely treat it as an 'explore the wilderness' campaign where civilization is the City-State of the World Emperor and the wilderness is everything north of the Sharryn River. Where could the adventurers' homebase be? Along the river or on the coast of Uther Pentwegern Sea?

3. Thunder Rift. I would change the scale of the map to make the rift larger. It would give me a place to put the Pit of Tortured Souls - the Dark Pit. I would also rewrite the history.

What do you think? Any other suggestions?

EDIT: As I went back through some previous posts to put tags on them, I saw my post about Barbarian Prince. I am going to take another look at that and see if that might work for a setting.