BEST? for what, every folding bike is a compromise in one way or the other for the most part. You have to first decide which are the attributes of the folding bike that are most important to you and will effect how easy it is for you to use and by extension how often. The Variables to consider besides the obvious COST are more unique to the designs and uses of folding bicycles.
Which of these 'special factors" is more important to you will naturally determine that factors influence in your choice of cycle.
The first factor for many people is ease of folding, My mom has a bike friday and she has to watch the video each time to review how to fold it up, it is not a simple process, then again Friday market their bikes as TRAVEL bikes not folding bikes don't they? The Giant Halfway folds down in less than 30 seconds, and the Bridgestone picnica folds up in less than 10 seconds !!
THE NEXT FACTOR related to folding is the size of space the bike takes up when folded and the weight.. either of these factors can make the bike a burden on public transit or even a pain to fit in the trunk of a car.
The final factor is the ride-ability of the bike, some folding bikes can never achieve the position that lead to comfort and efficiency, I rate folding bike ride ability on how long I am willing to ride it..at the bottom of the scale are bikes which are barely better than walking frustrating even in the discomfort they cause-the Abike comes to mind here, at the other end of the scale are folding bikes which I would be happy to tour on day after day.. most of the commercial folding bikes fit in the 2 hour ride at one go for my 6 foot tall size they may produce more comfortable results if your size is closer to the mean.
IN Short there is no answer to your question.. but another question... however I think if you keep these ideas in mind and ride/fold/as many bikes as possible you should be able to find the best bike for you and your needs..
Start by looking at Giant, KHS and Dahon
personal knowledge and experince