Reformation era sources, especially the Puritans, usually have more devotional value than ancient and medieval ones. One could be edified more by one volume of Matthew Henry's commentary than reading all that was written during the middle ages.
From ancient sources, though, the following are nice:
The sermons of Augustine, Basil, Chrysostom.
Athanasius's On the Incarnation.
Augustine's Confessions.
From medieval authors, anything by Bede, Wessel Gansfort, or Herve of Bourg-Dieu. Jerome of Prague and Jan Huss are nice as well, although not many works of their survive, and they're hard to come by.
The scholastics have no devotional value whatsoever. One would sooner be edified by watching paint dry than by reading Lombard, Bonaventure, Aquinas, Scotus, Ockham, Beale. Even Wycliffe is too scholastic to be of much devotional value, even though he's sounder than the rest.
The soundest pre-reformation Scripture expositions are those of the Greek Fathers (Theophylact, Theodoret, Oecumenius, and others; see the Catena Graecorum Patrum). Even Origen, for all his errors, actually had a pretty good understanding of justification in his writings on Romans. If one is deciding between a post-reformation commentator like Matthew Poole or Johannes Piscator and these pre-reformation writings it's not even a competition, but if one must have something older these are a lot better than, say, the Glossa Ordinaria, or Denis Carthusian, or Thomas's commentaries.