The English edition aimed at kids is dramatic and action-filled-
On the other hand, the English edition aimed at adults could be a Cold War spy thriller-
Meanwhile, the American edition seems to try to cut right down the middle and be a bit of both, but leaning heavily towards the kid's market-
It seems obvious that Bloomsbury, the English publisher, takes its' adult audience a bit more seriously than Scholastic, the American publisher. That's not a new story- the very first title in the series, "Harry Potter and the Philosopher's Stone" had its' title changed by Scholastic to "Harry Potter and the Sorcerer's Stone", because
they thought nobody in America would buy a book with the word "Philosopher" in it.
I think I like the American cover best though. In the end, the English kid's cover is too silly, and the Engish adult cover is too chilly- so the American cover must be "just right"...