My DC has offers from Teddies and Marlborough and I am struggling to pick between them. As a result, I have done a LOT of research on both. Also, Teddies is the most popular future school among students at my DC's current school.
Marlborough is oversubscribed at the moment but more bc it has a reputation as a happy, strong school with a wide variety of activities than anything to do with royals. Most of the potential future parents I have spoken to are hoping no royals attend since that will bring a lot more negatives (attention, security issues, media, etc)than positives (no doubt the royal offspring are very nice children, boost to the school's fame, etc)
Teddies does tend to clear out on the weekends but there is a strong, smallish core of mostly-overseas students who stay in so your child definitely wouldn't be alone. Another benefit is that it is located in the north end of Oxford, so student is not stuck out in the middle of nowhere but can (depending on school permission, of course) go into town for shopping, eating out, plays, concerts, museums, etc.
Yes, it is a strong school for sport at all levels, not just the A teams.
Teddies offers the IB as well as A levels. Some see this as a good thing but I do wonder if the school is spreading itself a bit thin - trying too hard to be all things to everyone.
The traffic in Oxford is rather awful but since Teddies is in the north end, it won't be as bad on Fridays at 1PM as if it were located right in the centre.
Oxford High or St. Helen & St. Katherine?