I usually would put my main one between the Grassy Plateaus and the Mushroom Forest biomes =D
Here:
(Ignore the black lines)
Southwestern Grassy Plateaus, near the Lifepod #17, on top of a spire.
Yo same
I usually build in the Grassy Plateaus.
Mushroom forest furthest from the aurora cause its got a portal to the alz and its in the middle of the map so it connects to multiple useful biomes
Underwater Islands
Dunes crater
My last base was built on the Floating Island.
At the entrance to the jellyshroom caves
Safe shallows was my first area
What do you think?