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If we're talking about heroes without the Allheroes mod, Laslo is the best, followed by Ellaina in second place, and Dugald in third. The others aren't that important, except maybe Vittorio for the Ballista or Axel for the Knights; Iris's Griffons won't have much of an impact. You might ask, why Laslo? Because after 4-5 weeks (or even sooner), the bonus from training and his skill will be around 40 Zealots. Just so you know, 200 Zealots dealing 7k damage per hit at level 15, without luck, will inflict significant damage on level 7 creatures; it's all in your hands. It's easier to start with Ellaina, and the Landlords with their resilience, native lands, battle frenzy, and luck are fast tanks that can take down even the most powerful enemy stacks with minimal losses. If you also manage to find a +2 HP ring, life will be good. Plus, for each peasant, you get +2 gold per day, which helps the hero level up quickly. After about two weeks, you'll have 200 peasants, which translates to +400 gold (a significant help). Dugald is good, but only for the "box" challenge, and even then, with the speed bonus. The benefit from archers is greater than from crossbowmen, but he's indispensable for the "box" challenge, as he can take down anything.