It totally depends what you are looking for but Holland House really wouldn't be an option for me unless you're looking for pure academia. It's very focused on sitting at desks at the front of the class learning and it's very very pushy with virtually no facilities and a tiny playground. Of course, if that's what you're looking for then it may be perfect.
I'm not a Goodwyns fan either, again, they have massive amounts of homework, far more than I feel is appropriate for young children, it's extremely strict and disciplined, I hate that they have 3 year olds in ties and blazers and it's very old fashioned. I have a lot of friends with children there and it's very split between those who adore that approach and those who are on waiting lists to get out asap. Again, have a look and see what you think.
Really sorry that I'm probably not giving you the answers you're looking for but from Stanmore I'd probably go for Radlett prep, I personally think it's in a totally different league to Holland House, it's just much broader, they have lovely grounds,learning is more modern in approach but gets results. They have a lovely theatre, good music facilities and I was sold on the children doing cycling proficiency when I went to visit. It offers much more in the way of extra curricular activities and I'd also seriously look at the travel time to Manor Lodge, everything I've heard about it makes we wish we lived a little bit closer so that we could consider it. You could also get to Edgegrove easily from there, I don't know what it's like academically but I know that pastorally it's meant to be very good.
If you're in stanmore you could also look at Orley Farm in Harrow and could easily get to to St Helens or Northwood College.