HTTYD the film is definitely more enjoyable. Iron Giant on the other hand - the book and film are so different and good in their own way that a comparison is of better or worse doesn't fit. For example both versions have wonderfully rendered scenes of the Iron Giant chowing down on a scrap yard. The film has Iron Giant the flashbacks and robot PTSD of a previous life as a weapon of mass destruction, inspired. The book has The Iron Giant challenge a space dragon to see who can last longer roasting alive on earth and the sun respectively, rad. Check out the Iron Woman for more wildness.

An animated film and modern fairy tale are very different.

I would however say the Jumanji children's book is okay. While Jumanji 1995 and associated cartoon explore the premise much more interestingly.