Determining the strongest Primarch in the Horus Heresy game is subjective, as each Primarch possesses unique abilities and strengths that can make them formidable opponents in different ways. Some might argue that Sanguinius, the angelic Primarch of the Blood Angels, or Angron, the ferocious Primarch of the World Eaters, are among the strongest in terms of raw power. Others may point to Magnus the Red, the psychic prodigy of the Thousand Sons, or Horus himself, whose martial prowess and strategic acumen made him the Warmaster. Ultimately, the "strongest" Primarch may vary depending on the specific context and the preferences of individual players.