I'm not sure what trails mean but either bike would be a great choice for "light" trails. something like hardpack gravel wouldn't pose a problem at all to you. Only stickler in your needs is to be able to carry it onto a bus. But if it's one of those greyhounds with a luggage compartment then it shouldn't be a problem at all planes and trains wouldn't be a prob either but for the plane you might need a case for it since they might throw it around. As for the train just have a giant el boso bag for the dahon and the montague bag for their bike. I'll probably vote for the montague because they actually say you are ok to use their bikes on mountain trails without a problem.

Good luck!