What type of cryptography should I use?

One time pads are impractical, and virtually impossible to use for normal use. As a note, we don't use them, nor do we know of anybody that does use them. They're just too difficult to use.

Steganography can be effective, but since it's not true cryptography, it's not really suitable for long-term use. If you keep sending hidden messages in picture files to somebody, eventually eavesdroppers may catch on, and figure out how to read your messages.

Symmetric ciphers, while very fast and very good, are difficult to use securely, since you have to share the key with somebody else for them to be useful.

That leaves public key ciphers. Some of the advantages of public key ciphers are:

• They do not require a secure line for transmitting a key. If you want to send a message to someone, you simply use that person's public key, which is already distributed as widely as possible.
• They permit verification (digital signatures).

To be fair, public key ciphers do have some disadvantages as well:

• Public keys must be verified, using a secure channel. Anybody could publish a public key claiming it belongs to you - someone using this key to encrypt a message to you would actually be encrypting it for the person who created that public key.
• Public key ciphers are more complex and difficult to implement.

The advantages of public key cryptography far outweigh the disadvantages. There are simple methods of verifying the authenticity of a public key (you can do it over the phone). And with the advent of powerful personal computers and mature cryptographic software, the complexity is much less of an issue now.

In summary, public key cryptography is the technique of choice for almost all common uses.