This image alone proves that HTTYD1 Toothless will always be scarier than in 2 and 3 (especially 3). He had his moments all throughout the first film yes, and all of them were absolutely spot on in getting us to be afraid of this very dangerous, unknown creature. But this image - this image.
Toothless has just tackled Stoick the Vast. Berk's most capable adversary against the dragons has been overpowered like it was nothing. And Toothless is about to end him.