I rode a Brompton before I bought a Dahon Jetstream P8. The Brompton folds extremely well, and would be the choice if I were carrying it on trains etc., but I was very disappointed by the ride. For me, it was twitchy, uncomfortable, and had an odd feeling that the rear wheel was tucked too far in under my centre of gravity. The Dahon is still a bit twitchy, but it rides almost like a conventional bike. The fold is not as small, but seeing as it only goes in the trunk of my car, that's not really an issue for me. The Dahon is as comfortable as any of my other machines.
I think that there is a definite relationship between the size of a folded bike and its rideability. Carrying larger quantities of luggage is not easy on folders, and that is a definite drawback for me.
