Nowhere is a good option. A bike can't fall over if its leaned on the ground, and in many cases you can lean a bike against a post or a tree if it needs to be kept upright.
On a more serious note, kickstands can crush bicycle tubes or can interfere with the crank or some other moving part if something goes wrong. Some frames are designed with kickstands in mind and have some reinforcements for kickstand installation. From this perspective, something like a Click-stand (like a folding tenting pole which can be used as a bike stand) is preferable.
If you insist on having a kickstand, check the bike's manual to see if theres a recommended spot. If not, a rear one is preferable for the interference reason, but you're more likely to find a center one legged kickstand easier, which is the one you'll probably install.