What it says on the tin. If your going to taken captive by a pre 1900 culture who is best and worst? I'm not saying being taken captive is a good thing, it's just, what is the least bad to worst. I'm also saying your not part of the "elite" who would get special treatment because of their place in the other society.
My Estimation:
Better: Societies that adopt a lot people, for example, the Mongols, Native Americans in general and the Iroqouis in particular. The French Canadians were also good at treating prisoners well.
Mixed: Raiders and most barbarian societies that, if you show your worth you have a chance to make something of yourself or you could have a life that is awful. If your kidnapped by Vikings you might end up the wife in a farmstead in Iceland, or you might end up being used for arrow practice.
Alternately, societies that will sacrifice you, but will treat you well, like the Aztecs, before they kill you.
Worst: Large scale slave societies like the Classical World and plantation societies like the American South. It is slightly worse if you add a racial component but only slightly worse.
What is your opinion?