Uniquely identifying records in CRMOD

For the exchange of data between CRMOD and several external systems it is important that we are able to uniquely identify a record in CRMOD.There are several fields that may be apllicable: RowID, Location, External ID. From the help documentation I get the feeling that the Row ID may change over time, for instance after a database schema change.
Which field should we use (for Accounts) to identify a certain record? This field should never change and should be a unique identifier. Ruud.