The August issue of Consumer Reports includes a brief test of five folding bicycles. Though there are many manufacturers of folders, they test one from each of the most popular brands. Their results and recommendations are incredibly the same as mine would be. And I didn't even get to ride any of the bikes.
They include folders from mainstream brands Trek and Giant in the test, but neither distinguishes itself. That is not surprising; the other manufacturers specialize in this type of bike, while Trek and Giant just added them to their product lines over the past few years. They probably sell a decent number to consumers who don't know about the better options on the market.
The Brompton C-Type C3E is recommended for people who plan to ride flat terrain and fold their bikes often. I concur, as long as you don't mind the $675 price tag for a bike of limited ability. Bromptons have a reputation for easy, compact folding, but their gearing and handling aren't the best. This is the only three-speed tested, but a model with more gears would be more expensive.
Bike Friday's claim to fame is that it rides like a regular bike. Consumer Reports tests the Stock Pocket Tourist (though more expensive than the others, it is Bike Friday's cheapest model) and agrees. Bike Friday's weakness as a folding bike is in the folding itself -- it's not the easiest or quickest to fold, and the result is not as compact as others. Though it is not the ideal commuter bike, it is a great travel bike. This is the only brand tested that could serve as an enthusiast's only bike. Bike Friday caters to that person, offering myriad customization options (at a price, of course).
Ultimately, Consumer Reports recommends the Dahon Speed D7. It is the least expensive bike tested, less than half the cost of a Bike Friday. It folds better than a Bike Friday but not as compactly as a Brompton. It performs a bit better than a Brompton but not as well as a Bike Friday. For a short-haul commuter bike that folds well, the Dahon is the best choice, and I say that despite being a biased Bike Friday owner. However, it is important to remember that just because the bikes all fold doesn't mean they are designed for the same purpose. If you want a bike that you can pack in a suitcase and fly to an out-of-town century ride (with no oversize charges), Bike Friday is one of the best you can buy, certainly the best one tested by Consumer Reports.