I Failed Restraint 101 Again......Drat.......
I suppose if you're going to put the case on the floor, it should be installed high.
If you're going to put the case on the desktop, then you should install it low in the case.
This of course makes a couple of assumptions: 1. this is an optical drive. 2. you don't feel like standing up every time you change a disc 3. the case offers you the option of either a high or low placement option 4.. I know what I'm talking about.
If this is a HDD we're talking about, stick it in the path of the front intake fan.
I'm rather partial to the optical drives being at the top, since all the store bought computers are like that. Hey, I'm brainwashed, what can I tell you.
Plan "B". Follow your heart, and stick it where you think it'll either make you feel good, or do the most good. Or possibly where it will make you the happiest.