As usual, these debates divide sharply down partisan lines, and I think Pixie hit on the major assessment point - when anyone was / is a teenager tends to inform the soundtrack of their lives, because that is when so many of life's formative experiences occur, and the music that soundtracks them becomes deeply rooted in the psyche.
I'm always wary of measuring the notion of 'popularity' because it's such a divisive way of measuring anything.
If you go by viewing figures - The X Factor is a 'better' show than Fawlty Towers, and straight away, you are nailing jelly to a wall.
Westlife had fourteen Number One singles, which sounds hugely impressive, until you consider that their entire combined sales for all their hits are not equal to the individual sales of any of The Beatles' Number Ones.
Since popularity is such a moveable feast, it does make for hugely enjoyable discussions, but at the end of the proverbial day, if any one decade is 'your' era, then that's the 'most popular' decade for you.