Same sex marriage should be enacted as a federal law under consideration of DOMA section 3's declaration as unconstitutional in stating marriage "means only a legal union between one man and one woman as husband and wife." With this removal, the federal government showed notice that marriage is not defined as only a union of opposite sex nor should it be regulated as such.
The federal government allows benefits to be obtained from legally wed same sex spouses including immigration, taxation, and federal employee health insurance. By recognizing same sex marriage and establishing benefit programs for such, the federal government is taking into consideration that it recognizes same sex marriage as a constitutional right and should thus be provided without limitation as a federal law.