What are the advantages and disadvantages of subject recruitment over the internet vs. through a recruiter hired specifically for this function (in-person recruiting) vs. through clinicians in a hospital setting?

What are the advantages and disadvantages of subject recruitment over the internet vs. through a recruiter hired specifically for this function (in-person recruiting) vs. through clinicians in a hospital setting? Does the disease or medical condition of interest make a difference? How else could you recruit for a clinical trial?