We live in headington and have lots of contact with friends/ colleagues at all local schools. DS is only preschool age so no first hand experience yet. As an added piece of info, i work in a childrens health setting locally.
headington girls: great school - good results and facilities. Not known anyone unhappy with it. Good mix of local girls and boarders from all sorts of backgrounds. Rounded girls emerge and go to a range of good universities. Occasionally bullying and stress related issues but not above what you would expect epidemiologically from a large girls school.
Oxford high girls: very selective and very highly pressured. Lots of stress related illness and especially high rate of anorexia. However, really bright robust girls do fantastically and achieve exceptional academic standards.
Rye st anthony - unfortunately seems to take kids who. Don't get into the other two schools. I rarely come across people with kids there. Visited earlier this year as they take boys in the pre prep. It seemed fine but nothing stood out to me.
St helen and st kats in abingdon: Great school with good facilities and high standard of results. Pressure wise in the middle of headington and oxford high.
Magdalen - takes girls in 6th form. Highly highly selective and pressurised. again only for super bright very robust kids. But if your child fits this bill they will probably get to oxbridge from MCS.
I personally would choose headington if / when i have a DD.
for the record we plan to go with new college for DS ....if he gets a place.
Hope that is useful.