The smart thing that Oliver Stone did with Platoon, was playing Samuel Barber's Adagio for Strings throughout the movie, including the end credits. The music is so sad, that it leaves viewers feeling like they have seen a much more emotionally powerful and distressing movie than what is actually the case.
Quentin Tarantino once said,
"Oliver Stone cheated. If you set Bill and Ted's Excellent Adventure to Adagio for Strings, you would still have an entire audience crying by the end of the movie."
Also, Oliver Stone initially wanted Platoon to be a purely factual account of the My Lai Massacre from March of 1968. He was going to tell the story of the American atrocities through the eyes of Paul Meadlo and Varnado Simpson... but after Simpson committed suicide because of sustained guilt over his involvement, Orion studios would no longer allow him to make that movie because they thought it would be too depressing.
As far as Full Metal Jacket is concerned, I loved the beginning of the movie from Parris Island. R. Lee Ermey should have won an Oscar ... but it got really boring after the movie shifted to Vietnam.
It's close. I guess I would go with FMJ.