I need help choosing the appropriate Metadata standard for a GDB for a local government. what are your recommendations and why ? what are the main differences between ISO 19139, ISO 19115 and FGDC.
First to separate ISO 19115 and 19139: Both describe the same. ISO 19115 ist the formal specification of a comprehensive set of metadata properties (some few, I think around 20, of them core metadata which are mandatory, and a huge set, I think some hundreds of optional metadata properties). ISO19139 is just a XML Schema File (XSD) which you can use to validate if a metadata set is valid ISO 19115, its an implementation in fact.
FGDC was specified before in the US, in my personal opinion its simpler.
The problem with ISO is: It was made to merge metadata from different providers, so this comprehensive property set came up, also with many possibilites to store the same in different properties. Nevertheless, every country derives its own profile of ISO 19115, so in most cases just the core metadata really can be merged together. Also attribute field documentation is not very intuitive in most ISO conformal Metadata Editors.
The problem with FGDC is: Probably its lacking properties you need for your documentation.
In fact you should ask yourself the following questions for choosing a standard:
In fact its a good idea to keep it simple. After messing around with Metadata standards for nearly 10 years (and no end in sight) a colleague of mine and I decided that its a good idea to throw all these standards over board and just document the things we need in a database. Open Data let us rethink the whole standardization theme, which really became just to complicated over the couple of years. Just choose the one editor in ArcCatalog that best fits your needs for documentation and information exchange.