If I try out different clicks and postulate which click I think works best that would be extremely subjective and I’m sure that different clicks work better for different practitioners. However, there are many fundamental qualities of a click signal that make the signal better suited for echolocation:
Signal Frequency. The frequency of a signal governs the resolution, in that a shorter wavelength (higher frequency) will give you more definition as to what it has bounced off of. Low frequency waves, since they have a longer wavelength are not as distinct. It has been said that the region of 3kHz is a good place to be for echolocating.
It is my hypothesis that a broad distribution of frequencies would be desirable (above a certain value) so that if some frequencies are absorbed by an object, others will be reflected by it.
Signal volume. The sound must be loud enough to stand out over ambient noise. 40 dB is about the level of quiet speech from a few feet away.
Clarity. This is probably one of the most, if not the most important property of the sound. It is critical that after the sound is made, there are no artifacts of the signal source still emitting sound. In other words, the sound must stop abruptly so that the reverberations can be clearly heard. If the sound were to taper off at all, this small amount of sound would easily cover up the reverberations, or at least create a confusing blend of signals.
Directional. If the signal is omni-directional, IE, if it is the same volume in all directions from the source, it will be difficult to know the direction from which it is being reflected, and thus where the object is that is doing the reflecting. Think of it like a flashlight. You can point a flashlight at one object and see what it is. Whereas, if you switch on a light bulb you are able to see everything in the room and there is more information to take in. When echolocating, we want to eliminate as much excess information as possible.