The Elemental Planes
The elemental planes overlap ours like a stack of maps, with a common geography across all of them.
The main difference is they element-swap:
FIRE replaces AIR and WATER
WATER replaces FIRE and EARTH
EARTH replaces AIR and WATER
AIR replaces FIRE and EARTH
Picture you are standing on the bank of a river and pop over to the Plane of Fire. The terrain is the same(ish) but the river of water is replaced with a river of fire. Also the air is on fire. If it rains, it rains fire droplets in the fire air. It's awful.
Now you pop over to the Plane of Air. The river is back, but there's no earth under your feet. It's just frigid cold air forever, with a river of water suspended in it. No sun hangs in the endless dark expanse. You can breathe, but you start to fall. Forever.
And so on.
In between worlds in the Prime Material Plane is an endless airless void. In the elemental planes this void is occupied is PURE elemental 'matter' in its most perfect form.
However, in the Axiomatic Planes this void doesn't exist; there is no real distance between the spaces in the Axiomatic Planes that correspond to worlds in the Prime Material Plane.
Travel between worlds in the Prime Material Plane could take centuries, or millennia, but if you pop over to one of the Axiomatic Planes you can skip all the space in between worlds and make the journey in hours.
You can't use the Plane of Concordant Opposition (true neutral) as that IS the void between worlds.
The chaotic planes (even the good ones) tend to drive the crews mad or twist the ships and crew into mutated horrors; the laws of reality are just too mutable.
The Heavenly planes are WAY to fortified against insertion. Trying to Skip through Elysium or the Seven Heavens results in a massive organized assault against the ship. So is Mechanus (l;awful neutral).
The Nine Hells (Lawful Evil) are almost as dangerous as the Seven Heavens but more willing to make deals; major shipping companies will bargain for safe passage through the realm. The option for planeskippers with lots of resources.
The Plane of Bleak Eternity (Neutral Evil) is kinda perfect for your average planeskipper; reality is fairly fixed but the inhabitants are just as likely to fight each other as notice the ship. Maybe you have to fight off a demon or two but it's quick and inexpensive...