Well... ...
Not counting Drow Armour and Cursed Armour, then AC wise... ...
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Armour of the Hart
-2 AC
Found in... ...
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the Underdark, in the Kuo-Toa Tunnels. The exact location, can be referenced
here, but I recommend you try to find it yourself.
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If not a Sorcerer, then a Paladin.