This post is not to refute Cecil’s answer, but to point out that there are other yardsticks to measure popularity by.
In the article Who was more popular, Elvis or the Beatles? dated 18 June, 1976, there are many questions posed. Who is most popular? Who had most consecutive hits? And who was on top the longest?
All of these questions are open to interpretation. Regarding ‘hits’, are we talking #1, top 10, or length on the charts? All are legitimate categories for measuring a record’s success. The ‘chart’ in question is the billboard chart, which is supposedly based on record sales (read: not necessarily retail sales). The record companies have long relied on actual radio airplay as a measurement of a records success. It can be argued that airplay could be factored into the equation.
Of course, an artist’s success can also be measured in marketing. Fan club membership, t-shirt sales, concert attendance & so on. For example, the Grateful Dead had only one song that could be considered for ‘hit’ status in chart assessment, and that was ‘Truckin’. Yet at the time the band broke up, they were the top grossing ($ in ticket sales) concert rock band. Obviously, they were wildly popular.
Being that the article is 28 years old, have some of these popularity parameters changed? These artists’ records are still in print. How many units have since been sold? How many times have their songs been covered? How many radio ‘plays’ have there been since. What are these artists’ libraries (the musical body of their work) worth?
Finally, the original article implies this question: What was these artists’ value or impact on popular culture? Impact on our culture can be another standard of measurement, although one harder to quantify. Both artists were anti-establishment for their time. Both, it can be argued, became established artists later in time. We’re all familiar with the bloated Vegas Pressley, but let us not forget Sir Paul McCartney. Comparisons of each artist’s impact on their respective generations would make an interesting article.