Hilton brands & outside the US

Hi all,

I have two questions. The first is how the different brands of Hilton in the US vary. Its easy to identify the top of the line Hilton brands, but what is the lowest brand? Doubletree? I have only stayed in HGIs and I am curious about the quality other brands offer for my upcoming trip and if there are any that should be avoided.

Secondly, how does Hilton compare with other chains in terms of locations and quality outside the US, specifically Europe and asia (mainly China and Japan).