that dr. jack said:
from my experience, COMLEX is way more straightforward clinically. they both give the same types of question stem, but ask different things. there's no molec cell bio on COMLEX, and very little biochem and genetics. some of the questions on COMLEX made me laugh because they were so easy (for example, the parents of a child with turner syndrome would have what chromosomal arrangements?), whereas on USMLE there were only a few that i answered in like 5 seconds or less. USMLE is also much more tricky and that kind of irked me because it felt like medical trivial pursuit at times.
overall, each exam reflects what each type of student is taught in their respective type of medical school.
it's also great to hear you are so impressed with the DOs you work with. for all the worrying that we all do while pre-med and in the first two years about MD vs. DO, once we get out into the hospitals and clinics, we realize no one really gives a $hit what letters are behind our names as long as we provide superior patient care. we have an MD student on our team right now and i feel we're all equal in terms of knowledge and clinical skill.