The best armour for defense is the Zeidrich;

Defence: 100
Defence %: 15
Magic Defence: 98
Magic Defence %: 18
Materia Slots: None
Growth: None
Notes: Strength +20, Magic +20, halves all elemental damage.

The best armour for magical defence is the Fourth Bracelet;

Defence: 74
Defence %: 3
Magic Defence: 100
Magic Defence %: 3
Materia Slots: O=O O=O O
Growth: Normal
Notes: Magic +20

The other good armours are;

Wizard Bracelet

Defence: 6
Defence %: 3
Magic Defence: 85
Magic Defence %: 3
Materia Slots: O=O O=O O=O O=O
Growth: Normal
Notes: Magic +20

Mystile

Defence: 65
Defence %: 50
Magic Defence: 72
Magic Defence %: 60
Materia Slots: O=O O=O O=O
Growth: Normal

Imperial Guard

Defence: 82
Defence %: 0
Magic Defence: 74
Magic Defence %: 0
Materia Slots: O=O O=O O=O
Growth: Normal

Aegis Armlet

Defence: 55
Defence %: 15
Magic Defence: 86
Magic Defence %: 50
Materia Slots: O=O O=O
Growth: Normal