What are ssh-keygen best practices?

Most users would simply type ssh-keygen and accept what they're given by default. But what are the best practices for generating ssh keys with ssh-keygen? For example: Use -o for the OpenSSH key format rather than the older PEM format (OpenSSH 6.5 introduced this feature years ago on 2014-01-30) (no longer needed since v7.8 in 2018-08) How should one calculate how many rounds of KDF to use with -a