According to UCLA Professor of Law Stephen Bainbridge,
Becker is a Nobel laureate in economics and well known academic who was one of the founders of the law and economics movement.
Posner is perhaps even better known former academic and current judge on the 7th Circuit US Court of Appeals. Even without a blog, Posner already was widely regarded as the most prolific legal writer of his day, issuing a flood of judicial opinions, law review articles, and books.
Should be an interesting read.
Update: In praise of Gary Becker.