Too many to choose from, but I’ll give you one per generation

Gen 1: Gyarados
Gen 2: Tyranitar
Gen 3: Latios
Gen 4: Garchomp
Gen 5: Volcarona
Gen 6: Noivern
Gen 7: Incineroar

Haven’t played after Gen 7

Infernape, Staraptor, Luxray, Floatzel, Garchomp, Lucario - can’t remember if this was Diamond or Platinum team