Interesting poll actually, really cool to see that visualised. However, I still fail to make the leap from "popular opinion" into "objective quality"- and I honestly suspect that you wouldn't be making that leap if it didn't agree with your personal feelings on the matter. Also, the survey tells us nothing about people's second favourite eras, or about overall views on each era. It is entirely possible, for instance, for two people to vote in identical ways and have an identical 'ranking' of eras, but one regards all three as VERY close (As I myself do), and another sees one as miles better than the second, which is miles better than the third. And that has a profound impact on how each era is viewed.
IE: It is possible to draw the conclusion that, for example, most U2 fans from earlier eras don't like the 00s very much at all, OR the conclusion that most U2 fans from earlier eras love the 00s but not *quite* as much. Both are equally valid interpretations. And neither tells us anything about objective quality.
I also wonder, incidentally, about what that tells us about the demographic here online, and how far that represents the average U2 fan. (For instance, a comparably small number from the 90s and 00s cite the 80s as their best decade, and yet Ithink a survey of most professional critical opinion would probably rank it first as Zooropa and Pop tend to be overlooked) Really a very interesting poll which you can very much go in-depth on!