I set the Pioneer tuner and the SKYFi to the same channel. I toggled the "A-B" switch and noticed a slight hum with the SKYFi. I attached a ground loop interrupter (GLI) between the SKYFi and the "A-B" switch. This eliminated the hum.
I toggled the "A-B" switch many times and I could not detect any difference in sound quality between the Pioneer and the SKYFi. They both sounded excellent. The toggle switch was so smooth that I wasn't even sure if it was really switching, so I turned off the Pioneer tuner, to make sure.
This is the best way to compare the tuners, because they are both playing the same song while connected to the same amplifier and speakers.
The difference in sound quality in other installations will be caused by the input device to the radio; the Blitzsafe and PIE connectors are superior over the FM modulated or cassette adapters. The output quality of the Pioneer and SKYFi tuner is the same, at least to my ears.