The fortress of Anvilring, located on a particularly sweet embark site.

Features:
Temperate warm forest biome.
A brook.
TONS of limestone.
Plenty of iron ore.
Some gold/silver/platinum, as well as tetrahedrite.
A Weaponsmith who is now Legendary (actually showed up as an early migrant).
An Armorsmith who is now a Grand Master (also showed up as an early migrant).
There are also a high-level metalcrafter and a pretty good mechanic.


Magma starts at Z-level -17.

Downsides:
No humans to trade with. Just dwarves and elves.
I'm not sure that there is a third cavern layer... and if there is, I think it's underwater. You do get the first and second layers, though.