Wait, looking at your first post, I'm assuming that you DON'T have a fan anywhere at all at the moment.
If that is the case, I strongly suggest the BACK of the case, not the front or side.
That is the most important place to put a fan, as having an intake fan blowing onto your CPU alone will cause hot air to stagnate on other parts of the computer case, which may be more disastrous. A slightly higher CPU temp will not cause any problems, however a burnt out PSU (which will happen, even though your PSU has a fan itself) will be disastrous.
Also, I'd like to point out to you that ALL cases come with back and front fan placements, but only some, and even then, only the newer cases will come with side fan placements. This is due to the fact that there is already enough cooling for the CPU with a single rear fan, and an extra side fan will further lower the temps, but will not have a huge impact on normal computing (overclockers excepted of course).
Then again, it is your computer, and if you still feel that a single side fan is adequate for your needs, feel free to do as your please