The most common admonition of the geneticist to the dog breeder is to "avoid the Popular Sire Syndrome". At the same time, the most common advice from breeder to breeder is "breed the best to best". So the conundrum is obvious and the consequence predictable - the "best" dogs are the most sought after, so they sire the most offspring and become popular sires.
The Popularity of Popular Sires
Even a century ago Williams Haynes (1915) was writing about the "Effect of the popular sire", noting that in three terrier breeds that he examined - Irish Terriers, Scottish Terriers, and Fox Terriers - about 40% of the puppies were sired by only 20% of the sires. Back then, "popularity" was quite different than now - his "prolific" dogs sired 5-7 litters, which would be completely unremarkable today. And surprisingly, Haynes thought that popular sires actually benefitted the breed by contributing to the preservation of variability in type.