I have Skull of ruin but yesterday i got hero surrender. The Skull of ruin give me more avoidance but hero surrender give me more armor and stamina.
I think its better skull of ruin for trash mob and hero surrender for boss???
Hero's Surrender gives you more avoidance, block is not avoidance.
But yeah, skull of ruin is nice for trash mobs, heroics, soloing etc, and Hero's Surrender is nice for bosses. Although Barricade of Eternity from Malygos 10 is even better, at least for most of current bosses.
Also, don't gem for parry, its less effective than gemming dodge. Not a very big difference, but still.