It really kind of depends on what you are looking for by reading them.
If you are looking for doctrinal writings- “The Faith of the Early Fathers” by Jurgens is outstanding (just volume 1 by itself is great).
If you are looking for longer writings for spiritual growth, etc. Then the New Advent website is great for having many of them in one place completely free.
If you are looking more for their commentary on the Gospels as part of a Bible study, then I would recommend “Catena Aurea”, Commentary on the Four Gospels, Collected Out of the Works of the Fathers compiled by St. Thomas Aquinas. There are four volumes, one for each Gospel, although they are not complete. For example Vol. 1 on Matthew only goes to Chapter 10 same with Luke Vol. 3 only to Chapter 10. Vol. 2 on Mark is complete. Lots of interesting views on different passages that sometimes leaves me speechless on how they could get so much out of seemingly so little.