Though I originally started my certification with ICEA I switched to CEA/MNY for the depth and breadth of study involved. Instead of a certification process you could zoom through easily, CEA's process required rigorous study and expectations. In addition to the higher standard of requirements, CEA offered accessible mentors in the NY area. The members of CEA are among the most dedicated, educated and knowledgeable group of women in the field. As a teacher-in-training you are required to audit classes with and learn from this devoted group of childbirth educators; this is an invaluable asset to CEA's educational program.
But I suppose if you're not in the NY area this is not an option; still I would look for a program where you can have direct interaction with your teachers, mentors and peers. This makes a huge difference in what type of teacher you become - because we learn best (sometimes) by observing others with more experience.