Underground so know one can find my base and i just love underground houses (it makes me feel safe underground) although i have all my animals and farms above ground a stay down In my lair just about always.
I always start by making a base underground because you have a chance of getting resources whilst digging it out and you can easily expand in as and when it's needed. Once I get myself established I usually create a smaller base above ground elsewhere for mining.
The Meaning of Life, the Universe, and Everything.
I always build my houses underground. Often just because I'll dig to bedrock and start mining as soon as I get a decent supply of wood, and I'll be down there so long that it turns into a camp which turns into a house. (Well, technically it's usually still just a shaft mine with some slightly nicer-looking rooms with stuff in them.) Although I'll often build a shed. For animals and excess supplies.
I always build above ground bases. Something about building a giant castle with all of my needs putting my personal stamp on the overworld that is satisfying. Of course I only play single player so that's part of why I can do that too. If I were playing on a server, I'd be underground.