How secret is it? How much effort do you want an adversary to spend vs. your intended recipient. How do you want to manage keys between yourself and the recipient? What is the size of the secret? How much do you trust the channels over which you are sending the message? Do you need to validate the identity of the secret's recipient? How many secrets do you need to send to how many recipients each minute?

All of these influence how the secret should be bundled up and sent, and it takes more than a library to pick the appropriate method.