Broadly stated, the brightest place on earth as viewed from the ISS is the Las Vegas strip.
All major the cities of the world are visible as clusters of bright spots from the ISS which is at an average altitude of 405 kilometers from earth.
The brightness observed depends on the cloud cover over an area under observation. The observed brightness also depends on the angle from which you make the observation. So if one were to take a shot over Mecca and Medina on a dark night in that locale, it might look like the brightest spots on that night. However, even then, other cities visible within the shot would not look dark. Earth never looks dark for any given length of time even from the altitude of the ISS which takes less than 45 minutes to pass over a whole side of the sphere of earth, and only a few seconds over the horizon visible to it at a given time since the ISS sees less than 5% of the area of earth at any given moment. So if one were to choose the right pass, the right angle and right shutter time for a shot, one can make Mecca and Medina look brighter than the surrounding visible cities none of which would appear completely dark.
If you were to go as far from earth as, say, the distance of Mars from earth, earth would look like a pin-head, more like a dull star, and moon even duller and smaller. Below is a photo of a view of earth and the moon as seen by NASA’s Curiosity science laboratory. Mecca and Medina have very little relevance even from a Martian view – let alone universal view.
Nevertheless, men will never stop arguing about whose father has the biggest testicles and whose place of worship is brighter.
For more on these arguments, I refer you to