Quick summary ...........
Brompton good small fold, small fit however, Mezzo rides bigger folds slightly bigger, less good on the rough, birdie better than most except the jetstream on the rough, folds smaller than the jetstream, but bigger folded than Mezzo or brompton. Dahon Curve tad bigger than Brompton folded, but rides better on rough,more of a pain to fold. Diblasi best bike to fold, availalbe in rust free SS but expensive for poor quality components. Downtube all models ride well fold about the same as the Dahon range, but cheaper. However downtube full suspension is no where near the quality of the Jetstream. Old moulton seperable difficult to find quickly, ride well, tad heavy,ride well on rough. Zoot Swift folds quite large, but thin, quality ride. Bike friday rides well, and specialize in fitting in a suitcase. Airimals are also good at later .IMO of course.......