Ive got a 20inch wheel Dahon speed folder but i am changing it soon for a mezzo. The reason being is that my work has just started the C2W scheme and i really want a bike that folds smaller. I commute into london on the trains and use the folder everyday i work.
Bromptons, the smallest fold but the ride i found to be poor compared to my dahon.
Mezzo, folds small enough and rides reasonably well.
Dahon 20incher, fold is massive, weighs a ton but rides much more like a real bike.