Suppose I had to choose among these 3 enchanted items (all of same quality), which would offer the best protection?

- one that fortifies light armor ( I wear light armor)

-one that fortifies block ( I use a shield)

-one that fortifies health

Block up to the cap.

Health after that.

Fortify [Armor] Skill enchantments are great for NPCs but almost worthless for PCs.

Fortify Block if you really need it I guess. Health is the way to go.

In my experience, the fortify health is the one that helps out tremendously, as an enchanting book helped me learn about that particular enchantment, book was very helpful in decision

Also depends on which type of character you are

Out of them I'd pick fortify block.
what you would need is fortify Magic resistance.