I have one dc at DAO in year 7. So far it seems v good. Children are kind to each other, appear motivated by their teachers, like the school and do well academically. There's a new head teacher and it will be interesting to see what changes she makes.
As a snapshot the school's progress score at GCSE is solidly strong rather than outstanding. Although the attainment scores are really very good. The students access a range of top flight universities when they leave, so an academic child at either DAO or Highgate would do just as well at either school probably.
I would imagine the DAO/Highgate cohort comes from broadly similar professional backgrounds. It seems a happy school with a huge amount of extracurricular options and is lucky to have the £900,000 funding per year from the worshipful company of brewers ( a partnership going back to the school's foundation back in the 17th century).
If I had any criticism to balance out the positives, I would say that the entry criteria really restricts entry for pupil premium children. The tiny catchment area (for the 22 local kids) doesn't really include social housing, and everyone else has either come in via the exam or music or being the younger sibling of a child who has got in through an exam route.
So perhaps DAO and Highgate will be very different in the next few years as the increased public focus on the role of schools as a driver of social mobility for disadvantaged children changes DAO's entry criteria. Only a good thing in my POV.
These are just my musings on the subject. Other than having a child in year seven at the school I have no other insight!
Hope it helps with your choice. Best of luck either way.