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There are good and bad physicians in both MD and DO categories. In regards to primary care fields (internal medicine, family practice, pediatrics, etc), I have seen excellence in both MD and DO. When it comes to specialty care, however, I have found more consistency in quality with MDs than DOs.
Whereas MD graduates have many programs to choose from when they specialize, DOs are often limited in their selection. Not only are there less programs within a specialty to select but the programs themselves are also usually smaller in size. Whether or not a smaller program is better or worse than a larger program is not always clear. In general, however, a larger program (more residents, more faculty, larger and better facilities, more patients, more rotations, more experiences, exposure to more difficult cases) will offer better training than a smaller program.
There is a perception that acceptance into a DO medical school is generally easier than into an MD program. I do not know how true this is.
Bottom line, for a PCP i would feel comfortable with both. For a specialist, I favor MDs. Regardless, research your physicians as thoroughly (if not more) as you research your ammunition, firearm, and gear.

Disclosure: I am an MD.