Ridley Scott, from the end of the Blue Ray audio commentary - I do hope they don't write essays about this in thirty years time. I'd rather they got it NOW, because it's all there.
A few interesting things from the writers commentary.
Fifield and Milburn were John Spaith's characters, and he, not Lindeloff, wrote the scene where they decide to leave the expedition when the first dead Engineer is found. Spaith's said there was a cut scene right after that that does show them get lost, despite the digital mapping, and argue about it.
Spaith's talks about all the reasons why you would never take your helmet off in a hostile environment, but states the actors and directors always want to find a way to remove them.
Lindeloff talks about the scene of Milburn petting the snake, and points out that it makes no sense because the previous scene of him finding the first life form was cut out. The commentary was done prior to the film's release, so even then he knew that scene was not going to play well the way the film was cut.
Spaith's talks about writing long and elaborate scenes where Shaw and Holloway find all kinds of clues and evidence, even within human DNA, indicating humans were engineered. Apparently none of it was filmed.