I chose to do an MD EM residency on several factors, of which some are intangible. I had never done an DO EM elective rotatoin, but did do my cores at a place that was "thinking of getting an IM/EM combined residency." Let me tell you, that this ED sees probably 15k a year, and is half run by DO FP attendings.
I also know of one DO EM residency that my friend was at, that either lost its accredidation or lost its funding, halfway through the year... she later had ot scramble into another DO EM residency, that purportedly is going to have funding/accredidation troubles.
You cannot go wrong with most MD EM residencies. MD residencies in general are under a lot more scrutiny than their DO counterparts.
That being said, there are a few good DO EM residencies out there. I believe Chicago has one. Doctor's in OH is also good. I also hear good things about a NY program whose name eludes me. There are good ones out there, though!
Q, DO