Ask HN: How do you manage your SSH keys?

Do you prefer tryping your passphrase every time you use them or you use an agent; if you use an agent, is it 'ssh-agent' or a frontend utility (e.g, Keychain)? If it is ssh-agent, how do you configure it? If it is a backend, what is it and why did you choose it? Please, tell us (me?) about your practices.