"Perfect waveform" for cross-correlations?
In general, the resolution of the cross correlation is proportional to the bandwidth of the signal. This is way pseudo-random signals are common for that purpose.
So if you are looking for a signal that will produce sharp and distinct cross-correlation, you should use such signals.  

However, if you are looking to improve the time-delay estimation for a given signal, you should pre-filter the signal with high-pass filter as the lower frequencies tend to produce more smooth cross correlation.