If you case has airflow issues, then using the second fan in the case is a better idea. If you only have a front fan, then put the second in the back to exhaust. You could try side exhaust if you have the option, if you already have front and back fans. If you have no case fans at all, indeed, put one in the front.
1 fan versu 2 fans is not a huge difference on the 212+, a couple degrees usually. If you case is lacking proper ventilation, it will have a far worse effect on the heat.