Defenses that have multiple ways to get potentially multiple extra cards per turn/block.
Some examples would be:
Pharisees: Proud Pharisee, Pretension, Damascus, Tenants Kill the Son
Babylonians: Dream, Swift Horses, Nebby, Bab Soldiers, Nimrod, Astrologers
Egyptians: Dreaming Pharaoh, Swift Horses, Egyptian Horses, Egyptian Magicians, Pharaoh's Baker, Broken Covenant (Pithom), 7 Years of Plenty
Those aren't the only "fast" defenses, just a few that come to mind right away. Obviously only a few of those cards are CBN/CBI and some (like Astrologers) aren't even guaranteed to get you an extra card, but the more options you include in the deck, the more likely you are to get some of them to work.