APT will always install the latest version that isn't excluded by preferences. Preferences are indicated in the file
/etc/apt/preferences (and in files under
Some repositories have a configuration that prevents their packages from being installed automatically. For example, the Debian backports have release files (which you can see in
/var/lib/apt/lists) that contain
If you have multiple sources for the exact same package (i.e. same package name, same version number), then APT downloads from the first source found in
/etc/apt/sources.list.d/*). So list local mirrors first. The order in
sources.list is irrelevant for packages that have a different version number.