Effective usage without unique key -- suggestion

Hi,

I am using postgresql 7.2.1 on redhat linux 7.3

I have a table in very high production database which is circulating
several thousands of records per day ie.. count does not exceed several
thousands.  Here for some technical reason i dont have unique key on this
table, but it should contain unique records. I know that without using
unique index it can be achieved in any of the following methods.

Method 1
-------- * check for the record. * if exists update, else insert

Method 2
-------- * delete the record (trigger on before insert) * insert the record

So Can you please suggest the best among the above 2 methods?

BTW, internals of the above 2 methods would be different. For example in
method 2, frequent deletion of records calls for vacuuming the database.  
FYI, i does VACUUM ANALYZE every day. So Can you please suggest the best
among the above 2 methods which well suits me and to use postgres more
effectively?

Suggestion or a link is suffice.
TIA.

regards,
bhuvaneswaran