I will definatly go with GUID in your situation, it require only one field and will provide uniqueness between your tables. I don't like multiple fields as PK because of the extra work they required.

HTH

>I am designing database for my new application. I think to use AutoNumber as PK, however, it will cause problem while replication. Do you think combination of AutoNumber and BrandID as PK is a good solution? Will it complicated coding? how about GUID?