I`d say the Brompton and the BF is two different bikes, so trying to agree on what is the best one is not realy comparable.
Brompton is for shorter trips and smaller fold and BF is for longer faster rides and not the smallest fold. Would make sense that a persons need, the area he rides in and the places he wants to take the bike (car boot, train, shops) and also size weight and shape of body makes it impossible to compare.
I`we got many bikes, and each one is best for its use. Guess I`d keep a BF- like folder if I could only keep one. If I lived car free in a town using PT a lot I guess I`d get a Brompton.