According to my experiences, upgrade success rate is 100% outside United States for both Hilton and Marriott even though for Gold members. I myself as a Hilton Diamond member, upgrade is only honored by Waldorf, Conrad, and some Hilton in the United States. As for DoubleTree I have ever stayed with in recent years, they don’t honor upgrade any more, especially after online check in and digital key feature was implemented. What’s worse is Doubletree don’t even do room pre assignment any more. You get what you pick at online check in not even to think about upgrade. Several times I did not do online check in to pick my own room, at check in I was put in the “leftover” rooms. I think Doubletree has become one of those other Hilton profiles that don’t offer upgrades such as Hampton Inn and Hilton Garden Inn.... Luxury hotel is the only way to go if you want to feel like a VIP today....