I have seen in Owens-Corning advertisements claims that glass fiber is better than mineral wool form NRC tests. The only comparison I have seen is in the CMHC document 02-108 where it is written:
Does anyone have a source for OC's claim that glass fiber is better than mineral fiber for filling walls?• Generally, at low frequencies, the increase in the transmission loss of a partition obtained by adding a sound absorptive material inside its cavity is equivalent regardless of the material used. Above 250 Hz, mineral fiber and blown cellulose give the best results; mineral fiber insulation provides slightly better transmission losses than glass fiber, especially around the critical frequency. Also, in the case of glass fiber, a greater transmission loss can be achieved by using denser batts.