How come Montague doesn't get into the discussion? I have a Prius, and it folds very well to fit into the back without limits. It's a full size bike and there are many positives over the others listed. It doesn't travel as well if you are taking the bus or train, but not everyone needs to meet those qualifications. Just wondering.
I say this, because I found a good deal on a brompton and bought it (amost a brand new bike, a 2010 M3L), and tho it is a work of art in my eyes, it doesn't compare to the Montague in purpose for me.
I have both a Montague and a Dahon. I love both bikes but the Dahon gets a lot more use. Having to remove the front tire to fold the Montague is a big pain in the neck while commuting. I think the Montague is the perfect bike to keep in the trunk (I don't even take the tire off to fold the Montague and put it in the trunk of my '06 Jetta). I also find the ride geometry of the Dahon to be more comfortable for my particular body type.
Regarding the Brompton- I take my bike on the commuter rail and I often see Dahon and Brompton owners here in Boston at North Station. They all look pretty happy with their bikes, FWIW