If you compare performance wise Decode and case.then there is not much differnces between them.Some time case is better and sometime Decode is better.It depend on CPU architecture .Case is easy to write and it have more readbility.

and if you compare IF ELSE with DECODE ,according to me Decode is much better than IF ElSE.

SQL> select * from emp
2 where ename = (case when ‘&&emp_name’ = ‘%’ then ename
3 else ‘&&emp_name’ end)
4 /
Enter value for emp_name: CAVE
old 2: where ename = (case when ‘&&emp_name’ = ‘%’ then ename
new 2: where ename = (case when ‘CAVE’ = ‘%’ then ename
old 3: else ‘&&emp_name’ end)
new 3: else ‘CAVE’ end)

EMPNO ENAME JOB MGR HIREDATE SAL COMM
———- ———- ——— ———- ——— ———- ———-
DEPTNO
———-
7844 CAVE SALESMAN 7698 08-SEP-81 1500 0
30

SQL>
SQL> undef emp_name
SQL> select * from emp
2 where ename = (case when ‘&&emp_name’ = ‘%’ then ename
3 else ‘&&emp_name’ end)
4 /
Enter value for emp_name: %
old 2: where ename = (case when ‘&&emp_name’ = ‘%’ then ename
new 2: where ename = (case when ‘%’ = ‘%’ then ename
old 3: else ‘&&emp_name’ end)
new 3: else ‘%’ end)

EMPNO ENAME JOB MGR HIREDATE SAL COMM
———- ———- ——— ———- ——— ———- ———-
DEPTNO
———-
7369 CLARKE CLERK 7902 17-DEC-80 800
20

7499 VAN WIJK SALESMAN 7698 20-FEB-81 1600 300
30

7521 PADFIELD SALESMAN 7698 22-FEB-81 1250 500
30

…