Honestly, it'd be easier to say which books have GOOD adaptations, since the norm is poor adaptations and it's hard to choose which one is the worst since so many suck in different ways.
1996 Matilda was faithful to Roald Dahl and brought the trunchbull to life in a way only movies can. Rest of cast was great but Trunchbull aces it, one of my favorite cinema villains of all time.