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There is no universally best primary stat. Each faction has its own strengths. Dungeon focuses on magic and attack, defense is not needed for Dungeon creatures. But humans happily increase both defense and attack, although they are weaker in magic (except for Axel the botanist, who increases knowledge faster than attack/defense).
P.S. You might as well ask what is better: ore or wood?;)
P.S. You might as well ask what is better: ore or wood?;)