[2020] which option do you choose for your base?

I tend to do some mix of the two. Often I just use a prefab to start with because it's there and relatively safe. Then as I progress I fabricate my horde shelter and main base underneath it. Occasionally I'll just reinforce the prefab i took over to start- depends on my mood.

That said, I have previously in my Fortitude only playthrough gone fully heavy armor and brawled with the horde out in a field, no traps, no buildings, just my fists, some buff items like beer, and many many undead zombies to re-dead.