* He was a gifted storyteller: Roald Dahl's imagination was a huge part of his success. This suggests he might have enjoyed English, where he could explore language and develop his writing skills.
* He was fascinated by the natural world: His stories often feature animals and fantastical creatures, indicating he might have been drawn to science or biology.
* He was a pilot during the war: This experience would have given him a strong interest in mechanics and engineering.
Ultimately, we can only speculate about his favorite subject. He was a complex individual with diverse interests. It's likely he found aspects of many subjects interesting, but it's impossible to say definitively which was his absolute favorite.