I’ve NC for this. It depends on what your aspirations are, Surrey preps are pretty varied. “Academic” here = aiming for scholarship level, a “normal” prep will still get you into the good secondaries albeit perhaps in second set not first. You can safely assume all the schools are good and in a bit of a bubble of high expectations compared to much of the country. Here’s some info on the ones I have seen / have children at / have children due to start at (in no particular order):
Downsend - well rounded school held in increasingly high regard. Sends lots to St Johns and Epsom, both of which are doing really well
Feltonfleet - expensive, good facilities, relaxed, not pushy, nice kids, could do better with results
Daneshill - expensive, amazing facilities, enormous (5 classes of 20 per year from Y2 I think?), competitive, a bit brash. Anyone in the middle 25-75% of school population can get a bit lost, hard to stand out in such a big crowd. However, you would probably get a place due to size and international families bring a bit more transient, big student body means huge variety of clubs and activities
Milbourne Lodge (mostly boys) - highly academic, has in the past been known as a hot house.. still quite pushy, gets good results, amazing work. Facilities shabby and run down, Victorian-Esque. New head seems to be making very good impression and positive changes, increasing number of girls starting. Unlikely you will get a place now
Parkside (boys) - great for sports, nice facilities, super nursery, not as academically rigorous by reputation
Notre Dame (girls but mixed to 7) - super facilities, lovely campus, very attentive staff, children seem happy but doesn’t have a strong academic reputation at senior level
Shrewsbury House prep (boys) and Pre-Prep (pretty much all boys), excellent school at prep level, great results, high achieving at sports too. Quite full on, impressive headmaster, broad and engaging curriculum in and outside the classroom. Often a back up for Kings entrants. The Pre-Prep in Esher has lovely nurturing environment and preps kids well but has been through a lot of staff changes recently
Rowan Girls - lovely school in Claygate, small and very highly regarded, feeds excellent girls schools including Guildford high and leh. Again a lot of staff changes at Pre-Prep level so seems a bit unsettled right now but not unusual, can happen anywhere
Claremont Fan Court - has always suffered from mixed reputation, assumed associations with Christian Science roots (not evident when I’ve seen it) and poor senior results. However it has beautiful grounds, most families there seem happy, and they are starting to be more selective. New head due in senior school this year should make a difference.
ACS - incredible facilities, enormous campus, more laid back than other schools. Very international student body, turns out some really lovely young people. However they teach to the IB syllabus so you need to be certain it’s what you want so as to be able to commit to it.
The only other one I can think of is CLFS which starts a bit later