Overall, Therian Forme Thundurus is different from Incarnate Forme Thundurus by having a higher attack power and only slightly less defense. The defensive stat differences are minor, but the attack boost the Therian Forme has makes it a better Pokémon. When picking between these two, we recommend the Therian Forme.

Is Tornadus Thundurus or Landorus better?

According to GamePress, Therian forme Tornadus' sacrifices attack for better defense while Landorus adds more attack while slightly reducing its defense in Therian forme. ... Thundurus has the same approach as Landorus, boosting its attack while minimally lowering its defense.

Which form of Tornadus is better?

Tornadus' Incarnate and Therian Forms have access to the same moves, but players may want to opt into different movesets on this new available form. Air Slash is the best choice for Tornadus' Fast Attack because Bite is more centered toward doing chip damage.