Black Dragons are versatile... good damage, but they cannot be buffed with magic and saved... except perhaps by expert Defense; essentially, this is a tank, not a DD, since all other units are fragile in terms of health. Manticores provide DPS and Minotaurs put out good damage, so it's better to take Defense — at expert level, that's 15% less of any damage, including ranged. Instead of a 30% bonus to Attack, level up Fire Magic and take Bloodlust at expert, or Berserk, or Blind with 25% retaliation power after blinding. The Shield (30% less contact damage) and Air Shield (50% against arrows) also matter, and with the expert Defense skill, this becomes very significant; if you also take three armor specialists... by level 20 there will be a bonus of 30% less of any damage... it's just insane... during a siege, 7 units couldn't kill one single Black Dragon of mine, while the hero was level 20 with 15 Attack. Draw your own conclusions. Attack is good if you always go first and wipe them out without retaliation; at 200%, this is often impossible.