The brompton for me is a slightly better bike, but I have to admit I'm curious about the Presto Lite.
I think brompton is a neater package, but it sometimes feels a bit heavy if you have to carry it a long way. The brompton has slightly bigger wheels and more tyre choice. Also the suspension gives it a theoretically superior ride. The brompton is also available as a six speed (mines a 10 speed!). In London every bike shop knows the brompton, whereas dahon dealers are much less common. It might be the opposite in the US.
There have been some improvements to the brompton recently - is a tiny bit lighter and about 30mm longer. There is also a rumour that an eight speed is on the way, once the sturmey archer/sunrace or Nexus8 narrow hubs become available.
The presto light is certainly that - light and could be carried a lot further before discomfort sets in - I would be tempted to try to make a rucksack like arrangement. The riding position is longer and probably better. The wheels and other components seem better quality. V-brakes are a much better option than the calliper brakes on the brompton. The smaller wheels probably run less freely on mixed surfaces and tyre availability may be a problem, although the primo comet fitted to the bike is anm excellent tyre. The aluminium frame may give a harsh ride together with small wheels and no suspension. Also you seem pretty stuck with 3 speed for now.

Just some ideas.