I don't know anything about Hendon Prep, but Edge Grove is lovely.
To me, it has a friendly, family feel. Lots of sport and extra-curricular activities but (under the new head) an increasing focus on academics too. Pastoral support is good, independence is encouraged, and the children are happy, enthusiastic and polite.
I have to say that the sport is brilliant at Edge Grove, and not just in the traditional sports. Some of the gifted children have reached a really high standard (ie UK rankings) but everyone has opportunities to represent their school in sport, not just the A team.
It's not only about the sport at Edge Grove but it does feel like quite an "outdoorsy" type of school iykwim. If you have an energetic child who doesn't mind getting a bit mucky (whether that's on the football pitch or poking around for spiders in a corner) then it would be perfect.
Not sure whether Slickrick's comments relate to a couple of years ago when there was a terrible headmaster at Edge Grove but the new guy seems great.
Good luck with your decision