The Frozen Shield can be considered more effective than the Ankh Shield during single-player boss fights, given that most boss encounters do not cause debuffs that can be prevented by the Ankh Shield, and the Paladin's Shield effect will not cause the player to take increased damage.

What's the best shield in Terraria?

The Ankh Shield is a Hardmode shield accessory which provides immunity to 12 / 11 / 10 different debuffs, knockback immunity, and an additional 4 defense.

Do shields stack in Terraria?

Dashing into enemies or getting hit will use up charges in the form of the spikes on the shield, which stack up to 3.