Here are the details, such as they are, for the sensor packages:
http://elite-dangerous.wikia.com/wiki/SensorsAs you see here and as well in game when an item is compared, the obvious difference is the range at which targets can be seen.
They all have the same integrity which I am assuming means the resistance to damage.
The missing information here is "what is the actual range vs optimal range" For example all weapons have a range of 3 km, but the optimal range is more like 2 km to actually hit the target and do damage. Yes you can hit something at 3 km but the weapons damage is not the same as when its at 2 km or less. Try hitting a moving target at that range with a cannon or a rail gun.
Although there are no stats for damage at max range vs optimal range and FD dropped the ball here as well.
So getting back to the optimal range of a sensor, I read this as the maximum range that I can see a target and its fully resolved IE, not blinking and flickering colors.