For 12X8 LED array with any 1 LED glowing at a time, should we charlieplex or use 74HC595n?
I love charlieplexing, perhaps too much.

Do you mean 'any one' or 'only one' LED on at a time?

With a 595 pin per LED, you can drive them continuously at high current, there is no reason why they should be dim. You can drive any combination of LEDs at full power.

With charlieplexing, if done niavely, then the best duty cycle you get is 1:N when there are N LEDs in your array, which is a huge brightness reduction. If 'only one' LED is to be on at any time, then it can be driven at full power. 

If you a bit more clever with charlieplexing, then you can approach a multiplex of 1:sqrt(N), to allow any combination of LEDs, or a few carefully chosen restricted combinations of LEDs at full power. 

You can regard charlieplexing as a conventional non-square multiplex with each column driven by an unused row. However, in this mode, if driven direct from the microcontroller pins, the current is limited to Ipin/number_of_columns. If you use a high current column driver, that rather defeats most of the saving of a charlieplex.