What everyone is trying to say is that radio wave propagation has more to do with range than modulation method.
That means that the frequency you are on and power you are running determine range, not so much the method of modulation. Sure, CW or SSB are readable a LITTLE farther than AM or FM - but not much!
In a situation where you ignore any other effect, use the transmitter output power. It attenuates with the square of the distance, but that can be calculated quite easily.
Assume some level of sensitivity at your receiver. When the antenna it is attached to receives that minimum level of power from the transmitter, then you are at the maximum range.
As you can see, the transmitter power out and the receiver sensitivity plus receive antenna gain all affect your calculation. Amateur radio groups have managed to get a signal transmitted at a 1 watt level and bounced off the moon - about 500,000 miles for that signal path.