I can only speak of 2 of the schools you mentioned.
Dragon School - we looked at it (some 6/7 years ago now). It was impressive and we kind of liked it but didnt love it. Probably an us thing rather than anything wrong with the school. Very mixed opinions when we asked around about it. It has a good academic record but for me prep school is about hell of alot more than that.
Abberley Hall - Is where our DC attended. I have been very impressed at this school. We nearly wiped it off out list of contenders partly because so few people had ever heard about it when we asked around for opinions and partly because for us it was a little further away than we wanted. This school IMO is a hidden gem of prep schools. It has a very academic record but caters for children across the spectrum. The head John Walker is a lovely very approachable man, down to earth and was always keen to speak to us, very fast at responding to phonecalls and emails even during the holidays no matter how trivial our query or matter. He also seemed to know an awful lot about my DC when we spoke.
The school is co-ed and run as a full boarding school although there are day children there. The Form 1's (year 4) are taught in their own block and very well cared for. The Form 1's have just moved into a brand new block. Each year group is streamed into Forms, there are typically 3 or 4 forms in each year. The Head likes to keep the Forms at around 12 pupils. I know one year, one of our DC would have been put into a form of 15 because of new children joining the year and immeadiately before the start of term we receved a letter explainong this and that they were going to ceate another form in the year group to keep the form numbers down. This I like. IMO, the children still have a healthy number of children in their year to mix with but with around 12 in a form, they get plenty of individual attention too.
I love this school it allowed my DC to be children but gave them great independence too. They are strict on manners and reguarly run annual competitions in speech and prose and by the time the children reach top year (year 8) they are good confident public speakers. The children are openly polite. Many times I have turned up at school on a random afternoon to visit my DC and pupils always politely greeted me, held open a door etc (just good general manners).
There are so many activities available included in the curriculum and optional extras its hard to list them all but my DC are very very different and both had many interests.
All subjects are subject specialist taught from Form 1. Modern languages include French and Spanish. Latin is also taught and Greek is taught to children in the top 2 forms from year 6.
DT, Art, Science, IT etc all taught in well equipped classrooms, the science block again is only 5 or so years old and better than alot of Senior schools we have recently looked at.
Very big on sport and games with matches on Saturdays and Wednesday.
The school also own a chalet in the French Alps and Year 5 children go for 2 to 3 weeks in the summer term and year 7 children go in the autumn terms again for 21/2 to 3 weeks. They are encouraged to speak as much as possbile in French when they are there. they recieve a variety of lessons in the chalet classroom as well as do lots of outdoor activities, shopping, french cooking etc as well. The children love it and they come back so much more confident in their French.
Another thing worth a mention is that this school does not rely on fundraising for improvements such a new buildings etc. It is all funded by the school and there is a plan in place of what they intend to build and improve with over the next few years. There have been several new developments and improvements to the school and its stunning grounds since we have been associated with the school and we just see it as being on the up and up.
Children come from far and wide. Alot of localish children from Hereforshire and Worcestershire, Shropshire and Wales. A fair number of children from London even (there is school transport and staff that accompany children to the station and on the train to London Paddington at exeats and half terms). There is also school transport on exeats to Chester and Cirencester. There are a few Korean children, a few Spanish children and some of the children are from military families.
Abberley feeds to many schools inc Winchester, Radley, Cheltenham College, Cheltenham Ladies, Malvern College, Malvern St James, Rugby, Gordonstoun and loads of others I just cant think of right now, but alot of well known names.
Please ask any questions, I am sure I can prattle on some more. 
Think I have said enough
(apologies for going on so long), but this school is worth a look, dont dismiss it due to it not being one of the top names being bounded about out there - go and look and see what you think.
Happy school hunting - I know it can be quite a minefield.