Optimal way to ignore duplicate inserts? [duplicate]

Question

This question already has an answer here:

• Idiomatic way to implement UPSERT in PostgreSQL 3 answers

Background

This problem relates to ignoring duplicate inserts using PostgreSQL 9.2 or greater. The reason I ask is because of this code:

  -- Ignores duplicates.
  INSERT INTO
    db_table (tbl_column_1, tbl_column_2)
  VALUES (
    SELECT
      unnseted_column,
      param_association
    FROM
      unnest( param_array_ids ) AS unnested_column
  );

The code is unencumbered by checks for existing values. (In this particular situation, the user does not care about errors from inserting duplicates -- the insertion should "just work".) Adding code in this situation to explicitly test for duplicates imparts complications.

Problem

In PostgreSQL, I have found a few ways to ignore duplicate inserts.

Ignore Duplicates #1

Create a transaction that catches unique constraint violations, taking no action:

  BEGIN
    INSERT INTO db_table (tbl_column) VALUES (v_tbl_column);
  EXCEPTION WHEN unique_violation THEN
    -- Ignore duplicate inserts.
  END;

Ignore Duplicates #2

Create a rule to ignore duplicates on a given table:

CREATE OR REPLACE RULE db_table_ignore_duplicate_inserts AS
    ON INSERT TO db_table
   WHERE (EXISTS ( SELECT 1
           FROM db_table
          WHERE db_table.tbl_column = NEW.tbl_column)) DO INSTEAD NOTHING;

Questions

My questions are mostly academic:

• What method is most efficient?
• What method is most maintainable, and why?
• What is the standard way to ignore insert duplication errors with PostgreSQL?
• Is there a technically more efficient way to ignore duplicate inserts; if so, what is it?

Thank you!