Dog
Dogs provide what researchers term conditional positive regard, though their conditions remain refreshingly transparent. A dog's assessment of human worth correlates directly with the proximity to scheduled feeding times and the presence of edible items in human hands. This evaluation system, whilst crude, offers predictable metrics that humans can interpret without ambiguity.
However, dogs exhibit what behavioural scientists describe as overwhelming bias towards approval. The average dog will express identical enthusiasm for an owner who has just closed a major business deal and one who has spent fourteen consecutive hours watching television. This consistency, whilst emotionally supportive, compromises the accuracy of the feedback mechanism.
Mirror
The mirror operates with what philosophers describe as brutal ontological neutrality. It reflects precisely what exists, without interpretation, context, or the social awareness that might prompt tactful omission. The physics involved, governed by the law of reflection, permits no negotiation. Angle of incidence equals angle of reflection, regardless of the observer's feelings about the result.
Research indicates that humans spend an average of 38 minutes daily consulting mirrors, seeking information they often find distressing. The mirror provides this distress without malice, without agenda, without the capacity to recognise that it has ruined someone's morning. It simply reports what is.
VERDICT
Dogs offer kindness at the expense of accuracy. Mirrors offer accuracy at the expense of kindness. For pure unfiltered truth, the mirror cannot be surpassed.