"The most popular choices for Medical College graduates this year were largely in primary care fields, which attracted 37.9 percent of graduates. These include pediatrics (12.6 percent); internal medicine (12.6 percent of the class); family medicine (10.2 percent of the class). The next top four choices were anesthesiology (9.2); emergency medicine (8.3 percent); surgery (7.8 percent); and radiology (5.3 percent).
Of the remaining 20 percent, specialties included orthopaedic surgery,
ophthalmology, radiation oncology, plastic surgery, pathology, radiology, neurology, neurosurgery, urology, physical medicine and rehabilitation, psychiatry, dermatology and otolaryngology."
http://www.mcw.edu/Releases/2011Releases/MatchDay2011.htm
As a comparison, for UCSF it looks like 53% of students went in to primary care residencies.
"Popular specialties among the class of 2011 (142 students) include: internal medicine (42 students), pediatrics (20 students), family medicine (14 students), and obstetrics-gynecology (14 students)."
http://www.ucsf.edu/news/2011/04/9764/successful-match-day-recruits-top-candidates-ucsf
I think it mainly depends on what you want to do and how hard you want to work.