I tend to agree with Tim on the GME part, although, in all fairness, it is hard to draw a comparison between ACGME and AOA residency programs because there are so few overall AOA residency programs when compared to allopathic programs. But most AOA programs are at small hospitals and that leaves one wondering if there is enough variety in the pathology encountered to give you a well rounded training. I think they are more than appropriate for family practice programs and general surgery, but it is possible that you will not get all the training you want if you are planning on a sub specialty of any kind. Then, again, I am only an MS3 and this is my impression at this time.
As for the 3rd and 4th years of medical school, being at a large medical center is not always what is touted to be. You are at the bottom of the pile. If there is a procedure to be done, the residents get the first pick, and they are all trying to get as many procedures as possible for their logs. So you can end up doing a lot of scut and very little of hands on. Following the entourage during morning rounds and being ingnored until it is time for some pimping is a stapple at major teaching hospitals. On the other hand, small community hospitals that don't have lots of residents or other med students offer you a chance to do lots of stuff and being more of an active member of an inservice team. Clinician offices, though lacking the "glamour" of inservice, actually give you a lot more volume and patient contact. It is important to do lots of inservice as you learn to manage the more complicated cases, but it is equally important to have a reasonable amount of office time, as you get used to seeing lots of patients and perfect your clinical skills.
Most allopathic schools will give their students huge chunks of inservice rotations and very little office, while DO schools, as a rule, will be heavier on the office time and lean on inservice. Neither is good. People who spend lots of time on inservice end up short on the basic physical assesment skills, hence residents out there that have trouble picking up stuff on physical exam but are fantastic at managing train wrecks in the ICU - they probably trained at major medical centers. On the other hand, others never miss even the most subtle grade 1 murmur but are totally stumped by ABGs - these probably spent a lot of time on office and clinic rotations...One should really strive to have a balanced education, which is easier said than done!