Docker, composer and ideal vendor dir location

Hello everyone, first of all a couple of reference links (if they are needed)

https://hub.docker.com/r/composer/composer

Specifically

Can be helpful in the case you want to override this in a particular environment such as vagrant or docker where you wouldn’t want this to be in a shared folder / volume.

OK, but what would be the ideal position?
For example, there are those who use /var/lib/vendor or /var/www/vendor

Nothinggggggggggggggg?