I think that all medical schools are looking for the same thing whether it is DO or MD: they are looking for a well rounded person who can handle the education and still be a functioning, compassionate doctor. I think that DOs put less stress on MCAT and GPA and more of an emphasis on an applicant that is compassionate and someone they feel would make a good Dr. Overall if I had to choose one aspect/factor it would be how the applicant presents themselves at the interview.
If you are asking about a factor pre-interview I would have to say that it is GPA/MCAT is important, but PS and EC are crucial. SO
in short: PS and ECs!