I liked the ending of the movie better than the book as well. I did watch the movie first and then read the book because I loved the movie, so my bias would certainly be towards the movie, but I felt that worked better. But they still kind of showcase the differences between book and movie, and how a movie will kind of have to move faster and show things on a more superficial level without diving into the psyche of a character in the same way.
The book ended without any building being bombed, and it ended with the narrator getting trapped is a double sense. He is thrown into a psychic ward, which is of course a real, physical entrapment. Also, it reveals that project mayhem halts, but the space monkeys only pauses until their leader returns, even though project mayhem could work perfectly without him. But the narrator does also get well again, but space monkeys are working at the ward, giving clear indication that they still recognize him as leader, which means that the narrator is still trapped because he knows that if he gets out of the ward, project mayhem will move on again, no matter what he does, so he is trapped in another sense as well.
The movie on the other end does not end this way, I suppose because that would be kind of a downer, but also, a ending that worked quite well in the book, would take relatively much more time when it is clear the movie is ending anyway, so they needed a quicker finale. But with the buildings exploding despite the narrators effort to avoid it, there still is the sense of project mayhem continuing, so the narrator is still trapped by his previous actions, although not physically confined of course.
Therefore I do think the endings are not that different anyway, because the fact whether a certain number of building explode or not is kinda beside the point. This also demonstrates the brilliant way Fincher and the writers did translate the book to the movie screen, even though they had to gloss a few things over, change some things and take a few shortcuts, they still stayed true to the spirit of the book.
But of course, seeing the credit card companies get blown to smithereens still appealed of course
