My favorite place to build a base is on the cliff side next to the south east entrance of the Water Cave with the turtles at grid 315.
With these mechanics in mind.
Reasons
1. It is on a small hilly cliff side so whenever scouts or raiders spawn, they always spawn on some flat ground far off where they get stuck on invisible walls. So you don't have to deal with constant attacks and not always stuck in a dreary cave. Occasionally once in a blue moon they manage to get you your base.
2. It located next to a ton of good flat building area. Within the 8 grid radius of grid 314 and grid 315 you have the entire Water Caves, you have the huge flat lands at the eastern Water Cave entrance which is located mostly in grid 335 and 355.
So you have a ton of building space and all your workers will still work since you're considered near them.
3. You can get most basic stuff you need.
If you place bear traps in the Water Cave it gives you deers and pigs. If you put the bear traps outside it gives sheep. So you can easily have an endless supply of meat, leather, poop, and wool without needing to creating breeding farms / pig farms if you're okay with gathering stuff manually.
If you place fish traps inside the cave you get Rock Fish which has 15 food value and doesn't need to be cooked, and if you have a NPC harvesting nearby the fish traps occassionally the game glitches out and gives you regular fish and shrimp. In the tiny pond at the south eastern entrance fish traps give you goldfish. If you put a harvesting NPC next to the pond with a Harvest Box you will have endless supply of goldfish.
You have plenty of room to plant trees all over the place so that you can chop them down whenever you need wood or sap.
Place gives you dirt when digging.
On reload or fast travel, there usually 1-2 Milky(s) / cows, and a bunch of Necks (ostriches) at grid 314 and 315. Which can be a positive or downside since they're hostile and will attack you.
4. Eventually when you start building inwards in the Water Cave you're mostly at grid 334 / 335 which means you're close enough to the flat area where the back entrance of the lab is at 353, 333, 334.
So eventually you can have like almost 5 seperate settlements always operating since they are all in the 8 square radius of you. One at the south western cave entrance, at 314, one at the south eastern cave entrance at 315, one at the eastern cave entrance at 355 and 335, one in the actual cave itself that is 334 and 335, and the back entrance of the lab at 353, 333, 334.
Or basically 1 mega city if you consider your settlements at the cave entrances and the cave itself as 1 settlement, and secondary base at the back entrance of the lab. Though both could also be considered 1 settlement also if you turn off invisible walls in the debug menu.
5. The walkway up to grids 314 and 294 makes a good roleplaying "checkpoint" place to build a little fort to deal with raids if you place a NPC with a decoy charm there.
6. The turtles in the Water Cave are on "Defender" status, so they only attack you and your stuff if you attack them first. Unlike the annoying bats and anglers in other caves.
Which makes it ideal place to build without having to worry about having to rebuild stuff or having your NPCs get attacked and depleting foodboxes by respawn enemies whenever you reload your save or fast travel. So you can just put all your tamed NPCs in there on Defend or Survivor mode and get free pet turtles.
Also since its inside most scouts and raids will just fizzle if you spend a lot of time in there if you don't have a decoy charm on some NPC elsewhere.
