I also think the digitech sounds better, but that said, I also think the volume setting of the digi harmonies are higher than the TC, allowing the harmonies to come through better ...
I think the real test would be to really lower the mp3 volume, make certain all fx and other settings are the same for both units, then lower the lead voice volume so that the VH can really be heard ... of course this is not how one would use the VH in a live or studio setting, but I think this will truly allow you to judge the two units ...