Which Orc hero do you prefer?

. And how is Krag better than Haghesh, who, after his first attack, turns into just another ordinary unit?

I will keep repeating this - read the manual! (because it clearly states: "...In addition, all of his attacks deal 5% more damage for each level of the hero." It is this, combined with "Devil Strike," that allows him to quickly eliminate groups of powerful units like dragons or cyclops, which Haghesh would struggle to kill with centaurs.