I've stayed at both the LAX Marriott and Westin recently, inbound and outbound from Vietnam. The Westin was much cheaper (on hotels.com; SPG has never come through for me on the best price "guarantee") and provided an adequate room and airport transportation. The Marriott was a shamefull mess, even in a "remodeled" room. See my review on TripAdvisor has details.
The AC would not lower the room temp below 75, and the lounge was beyond a joke. At 8 AM there was a line down the hall because the warden at the door was carefully scrutinizing her entry list like it was Club 54 in 1975. Once in there was no place to sit, but it didn't really matter because the buffet was totally empty anyway. One of the attendants was standing closely by, but her attention was on the business guy she was chatting up.
We ate at the airport.