Rules and Triggers: another question

Hi all.

Sorry to ask you another time this question.

Which one is the faster ?

If i write this trigger...
CREATE TRIGGER trigger_name
BEFORE DELETE
ON table_name
FOR EACH ROW EXECUTE PROCEDURE function();

and this rule:
CREATE RULE name_rule AS
ON DELETE TO table_name
DO select function();

When i delete values, which one will call the function the first ?

Someone can help me ??

And if I want to use only function, do I use Trigger or Rules ?

(Thanks to M. Michael Paesold to answer my question but I want another answer to be sure)

Best Regards.

Jérêom Chochon