The first three are good; if you've seen the movies you can definitely see where they stayed true to the first two books. The third book they cut a lot and I think is better than the movie. Don't get me wrong The Prisoner of Azakban is one of my favorites for the movies, but the book is way better.
I've never seen them with the adult covers, do you mean they have the movie on them? I'm not a fan of hardback books only because the price is high. Give me a paperback anyday!
Which are your favorite books?
For me it's: 1, 3, 6, and some of 7.