Vanguard Leather

Human chariots equip leather, but their so much weaker than knights, the T2 cav would still be a much stronger and  cheaper choice.  The T2 Marshall equips chain.  

Here are the Stats of Vanguard Leather Armor:

+20% Attack, -6% Cavalry Defense, -6% Spear Defense, -6% Bow Defense, and -6% Sword Defense

As you see, it makes great armor when attacking with T1 Cavalry, just wanted to point that out.

Human t1 cavalry do not require any armor to make, so they can be equipped with leather armor including vanguard armor.  Thus if you have a t1 cavalry commander (chariot) you can equip with leather armor and get a 20% attack bonus -- 40% if it's an elite division.  An elite division of chariots equipped with vanguard armor would be a pretty powerful force.  Personally, I just use it on my chariot commanders when I'm sending them out to attack as part of their training.  There's a small decrement to move speed, but chariots are pretty fast as it is.