EM is extremely challenging to get into, and as for "dime a dozen", that has the sound of insulting sarcasm.
Since I am doing my residency in EM, I don't think I would say residencies are as "plentiful" as PEDS or IM.
There are roughly 340 IM programs, 148 Orthopedic Surg programs,189 peds programs, and 118 EM programs, etc etc.
EM certainly has an aspect of Primary Care (this is NOT a bad word), but has huge aspects of IM, cardiology, psych, OB, peds, and Ortho. It is alot of fun, and one of the main reasons it is so popular, is that there is no call (makes residency much more tolerable) and each shift holds remarkable diversity.
The EM docs I have worked with have been the most intelligent and most fun people I have been around! Hell, the residents actually have a social life!
As for the best programs.
There is NO FORMAL LIST, but generally the most respected/oldest/best established are found in the following list:
U. of Cincy
U of Michigan
Indiana U.
Hennenpin County
Carolinas
Maricopa Med Center
MetroHealth (Cleveland)
Pittsburg
Christ Hospital
U. of Chicago
USC-LAC
Louisville
Vandy
Orlando
These programs consistantly work on research, maintain high visability within the field (SAEM, ACEP, AAEM) and lobby for standards and the rights of EM physicians.