Dilemma: where is Goblinburg?

So I have two ideas, and I don't know which one will suit the campaign better. This is me brainstorming.

Deep under Anatolia, circa 1630

History, Dumas style: factions like the crowns of Europe and the Company of Jesus join the Burgmeistress and the Guild of Sigil and Candle Peddlers.
Religions can include gods of ancient Summeria (I'm sure Turkey has lots of interesting stuff too, I'll have to research it) as well as different flavours of Reformed christianity.
Gunpowder aplenty!
A visit from the musketeer of Mars, maybe? Though I'm afraid he's busy saving La Rochelle with his team at this time.
Goblins are interbred descendants of mythological beings. It would be easy to come up with new types: korrigan, redcaps, bakemono, karankoncolos.
Ultimately I think of this as sword & sorcery & cloak & dagger & swash & buckle. It could really work but I'm worried about the amount of research I'd lose myself into. On the plus side, introducing new players would be easy: "after the siege of Arras, you fled to Marseilles, where you met a ship captain said she knew of a city where deserters like you could hide and thrive".

Inside a celestial object, long ago, somewhere dark and far away

This Space daemonic fantasy version is partly inspired by +Daniel Sell's Troika! which I was reading when thinking of this.
Cultists meet to worship dark gods from the outer voids, and roam city streets to carry out their insane demands.
Goblins are star children, born of drifting seeds, daemonspawn, genetic experiments.
Magic and science are the same thing, with a lot of heat rifles and brains in jars and psychomathematic grimoires.
The Rays come from some sort of crystal dome in the asteroid; it amplifies the light of passing stars. Day/night cycles on the bright side of Goblinburg are very random (think maybe d20+d10 hours of light or darkness).
The New Worlds above Goblinburg are caves filled with alien flora. Above then is the cold, dead surface, where impossible treasure awaits in some kind of abandoned space station.
Strangely enough, this version of Goblinburg would be closer to straight fantasy (at least until the surface station is discovered, when it would morph into spelljammer hexploration). The city survives in isolation, barred the odd portal. I don't think I mind - it's a big enough place to keep everyone's interest. I also think the most claustrophobic of players - the people who always want to go outside of the sandbox - would have an escape route via portals. I have both Red & Pleasant Land and Maze of the Blue Medusa. If they want to step out, they're welcome to step into that mirror or painting. That'll learn 'em.

So here we are. I thought writing down the pros and cons of both ideas would help me decide. It hasn't. I have analysis paralysis, you guys.