ROWNUM = 1 to replace count(*)

For a long time, I have been using the EXISTS clause to determine if at least one record exists in a given table for a given condition. for example - if I wanted to see if an employee by lastname = 'smith' exists in the "employee" table, I used the following query

select 1

  into v_exists_flag

  from dual

 where exists (select 1

                 from employee

                where lastname = 'smith'

              )

This is definitely more efficient than using the count(*) clause.

select count(*)

  into v_count

  from employee

 where lastname = 'smith'

if v_count > 0 then....

But, recently someone mentioned that using ROWNUM = 1 has better performance than using the EXISTS clause as shown below

select 1

  into v_count

  from employee

 where lastname = 'smith'

   and rownum = 1