The best ending in Dragon Age: The Veilguard is the one where all but one member of your team survives, and no Faction leaders die. Davrin or Harding's death is unfortunately unavoidable, as whoever you pick to lead the second team during the 'Isle of the Gods' main quest will die later on, no matter what.

The Veilguard puts player choice at the forefront as your decisions and choices can dramatically affect how the game plays out and reaches its