Underground vs. Overground bases

I'm not looking for one or the other because that is subjective instead what are the good points and bad points of each?

e.g. Overground are easier to see. Underground had less access for mobs to get inside.

I've only been playing Minecraft for about a month now, but for offline play, I find that it is best to make a "home" that is both above and below ground.

Start out by creating an above ground fortress in a place close to your spawn point. I created a log cabin, which slowly became bigger and bigger. I found that once I had the basic house complete, it was beneficial to spend the night hours digging deeper and deeper into the ground (of course leaving torches everywhere!). Not only does this give you something to do while it's dark out, but it also gives your fortress plenty of places to hide and block off incoming threats.

I assume online if your home is taken over by griefers, you can block off part of it and hide within your underground area.

Remember that all dark areas can spawn enemies, so torches are a must. Collect wood in the day to create sticks and you will get plenty of coal by digging into the ground. Always carry a weapon with you, because you can dig a block out that has an underground DARK cavern with plenty of spiders and zombies in it. In this case be ready to fight, or block it back up quickly before you're killed with arrows!

If you feel it necessary, build a huge "antennae" on the roof of your complex and put torches on it. If you die, or get lost, this should help you get back!

That might be a lot of information that everyone knows already, but I hope I helped.

If you construct proper doors and walls, and keep all light in your base at least an "8", there is no difference between aboveground and belowground.

For a while, post halloween update, mobs spawned at higher light levels at lower depths. Now that this is no longer the case, the vertical position of your little slice of Minecraft heaven doesn't matter.

I personally prefer a 3-tiered base: underground, on ground, and a third floating tier. Most important things can be done in any tier, but combining the three gives redundancy and a variety of unique advantages. Of course, there are techniques for mitigating many of the cons of each tier, as well.

(I should note, this is only taking single-player into account.)

A rough, inexhaustive overview of each tier's pros/cons:

-Underground-

Pros:

• Easy to expand
• Rare materials are more accessible
• Not prone to catching fire

Cons:

• Expansion dangers, such as mobs and lava
• Staple materials (such as wood) have to be brought down by hand, at least at first

-On Ground-

Pros:

• Easy access to many staple materials (food, wood)
• Simple to expand

Cons:

• Exposed to the elements and mobs
• Most easily damaged by Creepers

-Floating-

Pros:

• Largely immune to mob damage
• Great views

Cons:

• Most complicated to build
• Most prone to lightning strikes

Underground bases make it easier to hide your chests of goodies and the base itself from griefers.

This is a huge advantage on servers with a high incidents of griefers/theives.

Don't tell anyone, but the ladder down to my base is hidden under a patch of cactus. =)