Fireguard has better dps and stats, but Inuuro's has expertise, which is pretty important for any tank (the defense rating is a nice touch, but I'm more concerned with the expertise rating).

Expertise rating reduces the chance that enemies will dodge or parry your attacks. Reducing or eliminating parries is pretty important because a parry reduces the swing timer of the next attack by up to 40%. You don't want hard hitting bosses to hit up to 40% faster, so you want to reduce their chance to parry. This is also why it's extremely important for melee dps to fight a boss from behind, because parry only works on frontal attacks. Also, less dodges and parries means you land more attacks, increasing your threat.

Inuuro's Blade is also much cheaper and easier to acquire. You only need to be revered with the Shattered Sun to buy Inuuro's, where as you need to be a Blacksmith to craft and use Fireguard (Inuuro's Blade costs 43 gold, Fireguard costs several hundred).