That I know the three auto-update options are:
My doubt is about the auto_update_core_dev is it some kind of "developer" updates with beta features, something reserved for developers to test if news things works or not?
This was near impossible for me to find out from the documentation, but digging through the code, it would appear that auto_update_core_dev allows for automatic updates to versions containing a dash (-).
$current_is_development_version = (bool) strpos( $wp_version, '-' );
https://github.com/WordPress/WordPress/blob/master/wp-admin/includes/class-core-upgrader.php#L279
Further down, you will also see a comment with some examples of versions that are considered part of the dev branch.
// 3: 3.7-alpha-25000 -> 3.7-alpha-25678 -> 3.7-beta1 -> 3.7-beta2.
if ( $current_is_development_version ) {
https://github.com/WordPress/WordPress/blob/master/wp-admin/includes/class-core-upgrader.php#L340
I'm going to assume you'd want that turned off.