Use content types:
Content Types should be created at the highest site level possible. If the content type you want to build requires site columns from the Site Collection Site Columns Gallery AND some site columns from a SubSite’s Site Columns Gallery, the Content Type would need to be created at the SubSite level.
It’s a push down approach. he Parent contributes DNA to the child. The Child cannot contribute DNA to a Parent.
But sometimes the top level will be “crowded” with content types. So have a Content type hub.