SQL from/where or join?
If you are asking whether it is more efficient to use SQL 92 join syntax

SELECT empno, ename, dname
  FROM emp
       JOIN dept USING (deptno)


or to use the older join syntax

SELECT empno, ename, dname
  FROM emp  e,
       dept d
 WHERE e.deptno = d.deptno


the answer is that it doesn't matter.  The optimizer is automatically going to do an internal transformation from the SQL 92 syntax to the older syntax anyway.

If you have performance problems, it is highly unlikely that they are related to your choice of join syntax (though when Oracle first added support for SQL 92 join syntax, there were bugs relating to its ability to transform the SQL into the older style).