The Granary is the café equivalent of a comfortable chair, nothing showy, consistently good, and used by locals as much as visitors. Broad Street brunch with decent coffee and honest food after a morning in the bookshops is close to the ideal Hay-on-Wye activity.
It fills up on busy Hay Festival days, so arrive early or go off-peak. The kind of place that anchors a day rather than being the destination itself.