They are all good schools, but very different. You need to decide what you are looking for in a school.
My impressions (having visited them all and talked to people with girls at each) were:
- Surbiton High :
All-through removes the 11+ angst. However, both the others send lots of girls to SHS for senior school, so that would probably be one of your default/fallback options anyway.
It's a really, really big school. Academically fine but not all that selective. Sports, music etc all as you would expect. Seems to be a big emphasis on Art. It's a town-centre school, so not a lot of green space but very convenient (and good buses for the girls).
- Holy Cross:
Absolutely beautiful, idyllic environment. Good academics, but very pastoral. There's a very strong Catholic emphasis though, so it depends whether you are comfortable with that. They are quite open to families of different faiths, but I'm not sure an atheist family would feel comfortable with how deeply religion runs through the school.
- The Study:
Lovely, but very traditional prep school (Very posh). Very strong academics : gets girls into great senior schools. Quite small. Half-day Fridays might be difficult for working parents (I got the impression most mums were SAH - but this might be completely wrong).
Have you considered other local options?
If you want strong academics, Wimbledon High School or Putney High School? They are quite high pressure though.
Another local option is the Hall School. It's a marmite school: reputation for behaviour not being as good, but some people love it's relaxed attitude (no technology, a retreat in Wales where the children go for weekends away). It's co-ed.
A bit further afield is Rowan Prep School in Claygate, which is fantastic. Very strong academics (great destinations) and strong sports, all in a lovely environment. It's a brilliantly run school which nurtures and challenges the girls all at the same time.
There are so many fantastic options in the area. Hope you are able to find a good fit for your daughter.