Most readable way to display key value pairs

I am designing an app which has lots of data on any given screen, I've search Google and UX stack exchange and can't seem to find anything (perhaps I'm phrasing my search term wrong).

Is there any research into best practise for displaying a list of key value pairs?

Approach A - right align keys, left align value

        Key: Value
 Longer Key: Value
  Short Key: Value that could be long

Approach B - Left align keys, right align value

Key:                              Value
Longer Key:                       Value
Short Key:     Value that could be long

Approach C - Left align both

Key: Value
Longer Key: Value
Short Key: Value that could be long

Approach D - something else?

I'd be interested to know what the anecdotal best practise is here, and bonus points for actual research/testing of the best approach.