As a DO, you a required to take the COMLEX for licensure. Some DO students choose to take the USMLE since it is graded differently than the COMLEX. This way it is easier for program directors to compare the DO students to MD students. In addition, some programs require you to have at least taken the USMLE step 1 regardless of whether you are a DO or MD. In most instances, as a DO student it will suffice to just take USMLE step 1.
One example is Denver's Emergency medicine program. I contacted the PD and he told me that they base their admission on 7 criteria (i.e. med school, clinical grades, etc. plus USMLE step 1 scores). When I asked him if COMLEX step 1 or even if I took USMLE step 2 as an alternative would be adequate, he said that only USMLE step 1 was evaluated in their criteria. As such, w/o USMLE step 1 scores, my app would only be evaluated based on the other six criteria. This seems like a big disadvantage, thus the reason for my previous statement.
What about taking USMLE Steps 1 & 2? Of course everyone says you should take USMLE if you are trying to get into a competetive allopathic residency. Does this include Step 2? Or is a good step 1 sufficient?