I regularly stay at the Islington Hilton (previously as a Gold) and have been treated very well - I always get one of the two rooms I really like or occasionally one of their suites. This may, however, be because I stay there 12 times a year as well as being Gold.
I've had some excellent room upgrades as a Gold, but sometimes they have been matched by nothing else but the upgrade.
I think that apart from Islington, the best treatment has come from Prague, Barcelona and Cairns.
The worst has been Leicester, Leeds and Melbourne.
I await to see what my one year as Diamond brings me (and yes, I am planning a decent on Rome).