I love 1/2 mils. I always think if its on the map you can definately see it on the ground (apart from Bagshot Mast - I wish they would paint a nice big yellow square next to it).
I always found the 1/4 mils too fussy with too much info on them and ground features you couldn't see. They may have changed recently but that was my memory. Also you run out of map too quickly on long cross countries.
I agree with the comment about the US terminal charts, they are great although its hard to remember a thumb is only 5 miles, not 10. I believe they are going to produce similar charts for the London area soon.