As a piezo buzzer is mainly capacitive , you can add a series inductor to it to shape the pulse closer to a resonant sine,
The balance comes from the role of the buzzer, anything that "warbles" between 2-4Khz is extremely hard for us humans to ignore,
If you just want to notify someone, then pure tone "pip"s tend to be the least offensive. around 2Khz,
If you want someone to be unable to ignore it, square wave, that varies about 200Hz at 4Khz. (vary the pulse width) about 1 second on, 2 seconds off.