Hilton recently changed its policy to become more competitive with Starwood (Sheraton) and now states:
Diamond HHonors guests will receive upgrades to preferred rooms, based on availability for the entire stay at the time of check-in. Upgrades for Diamond HHonors guests may include the next-best available room from the room type booked. Upgrades may also be rooms with desirable views, corner rooms, rooms on high floors, rooms with special amenities, rooms on Executive Floors**, or suites, as identified by each property. Some exclusions based on rate and room type may apply.
As a consequence, we enjoyed being thoroughly spoiled with significantly enhanced lodgings at the Hilton Vienna Plaza, Hilton Budapest WestEnd, Hilton Budapest, Bratislava Doubletree, and the Zurich Airport Hilton.
Starwood also looked after us. We were also treated magnificently both times at the Sheraton Bratislava, the second stay with an amazing top-floor suite.
Our only slightly disappointing experience was at the Hilton Vienna (Stadtpark), where we not only were given a basic small room, but, of far greater concern, one that was far too warm.
Vienna was enjoying unseasonably warm and sunny weather in mid-March that we enjoyed during the day but suffered through the first night since the hotel's air conditioning hadn't been turned on.
A helpful young Executive Lounge manager toured us around several rooms the second afternoon (she empathized because the lounge itself - one floor up and facing the same afternoon sun as our room - was also far too warm), and we bypassed two suites to choose a room on the other side of the hotel that was at least passably less warm.
That room, although not a suite, was a significant upgrade from our first basic room, and we raise our eyebrows at the thought that an "upgraded" room hadn't been available the previous night. Still, it's possible but we're left with the impression that every other hotel was trying harder to comply with Hilton's new policy.
Finally, in the great scheme of things, if that was the "worst" hotel night of our entire trip, we don't have much to complain about at all.
In fact, it was all fantastic.