Decoupling has to do with preventing noise generated by a device to get back into the power plane. Therefor high insersion loss is required. Example for good decoupling devices are the Murata NFM series if devices. For bypass capacitors the main criteria is to provide enough energy to overcome short and long power spikes created by active switching components such as an IC. The power profile (spikes) have to be matched by selecting appropropriate capacitors that are effecitve for short or long power draws.
