Mum:
I was 14 when my nonN father left my N mother. After six months of living alone with her, and with no small help from my therapist (which, ironically, I had begun to see because of the psychosomatic ulcer I had developed due to my mother's abuse), I made the choice to live with my father.
At that time she was living in a nice house roughly half a mile from my school. My father was living in an apartment with a 45-minute commute to town and a neighbor that spent a significant amount of time blaring something the sounded suspiciously like carnival music. With my mother I had my own bedroom, entertainment room, and bathroom... and never a single moment of privacy that wasn't accompanied by my mother banging on the locked door crying her eyes out. With my father I slept on a leaky air mattress in a room that doubled as a storage space for stained glass... I consider a sliver of glass in my foot every six months adequate payment for finally being able to dance around in my room without the fear of being watched.
Living with my father wasn't, and still isn't, a fairly tale. The years of being married to my mother made him afraid to assert any parental authority and unable to accept criticism. Furthermore, because he had trouble admitting to himself that my mother was as bad as she was, it took six years for him to stop pushing me to make a reconciliation. This all was made doubly hard by the fact that I had a strong case of hero worship regarding my father (he had, after all, given me a place to go). It was devastating to face just how human he was and how deep his scars ran.
The point I am attempting to illustrate through rather babbly means is this:
Living with my dad was hard and hurt like hell on a regular basis. Since I moved in with him I've been forced to deal with my feelings, learn to assert myself, accept other's imperfections, and spot broken glass while attempting to execute an off-balance pirouette.
Living with my mother was physically comfortable and spiritually destructive. Had I stayed with her, I have no doubt that what little strength I still had would have been crushed out of me, along with any chance I had to teach myself to seek peace and happiness.
I can't say it would be the same for everybody. I had a damn good therapist and was both old enough and self-aware enough to know that my house was dangerous. I would like to believe, however, that in a situation with a nonN parent and child who are aware enough to leave an N dynamic, that they will also be able to avoid the brunt of the pain and abuse generated by said dynamic.