update/insert, delete/insert efficiency WRT vacuum and MVCC

Is there a difference in PostgreSQL performance between these two
different strategies:

if(!exec("update foo set bar='blahblah' where name = 'xx'"))
exec("insert into foo(name, bar) values('xx','blahblah'");
or
exec("delete from foo where name = 'xx'");
exec("insert into foo(name, bar) values('xx','blahblah'");

In my session handler code I can do either, but am curious if it makes any
difference. Yes, "name" is unique.