As far as I can tell, both syntaxes are equivalent. The first is SQL standard, the second is MySQL’s extension.
So they should be exactly equivalent performance wise.
http://dev.mysql.com/doc/refman/5.6/en/insert.html says:
INSERT inserts new rows into an existing table. The INSERT … VALUES and INSERT … SET forms of the statement insert rows based on explicitly specified values. The INSERT … SELECT form inserts rows selected from another table or tables.