i chose to write in a storylike format... i wrote about my journey to PT. i started with my background & tried to point out how it was unique versus other applicants.... how my upbringing shaped my personality to be in-line with this profession. i described some developmental missteps and how those experiences actually ended up steering me toward the career i believe is meant to be for me. anytime you mention something that may be perceived as negative, make sure you describe it as a learning experience. i hesitate to give you much pointed or even advice because my success in applications has been hit-or-miss... but what i've described above is basically what i did in my autobiographical essay. focus more on the personal developments than on the professional which should've been moreso the subject in the statement of purpose. you can obviously (and probably should) tie in how those personal developments connect to your professional goals, but don't make it the primary for this essay.
hopefully you get some other responses in case people agree or disagree with me. just know that there is no absolute right way to do this. the essays are a way for admissions to get to know the applicant better, so write something truthful and compelling that will make them interested in you.