Basically as indicated above, at the moment all folders are a compromise between fold and performance.
Did a daily commute from Victoria to Kings Cross and back for around 3 years on a folder. I had a Dahon Jetstream for most of that time which rode brilliantly (to the extent that I also did a few much longer road rides on it at the weekend), but as others have said it was really bulky folded up and a bit of a pain to get onto crowded trains.
I tried Bromptons too, loved the fold, but as a big guy really struggled with them – too flexy and unstable by far.
20″ bikes like Dahon, Birdy, Bike Friday etc ride more like “proper” bikes but don’t have such a compact fold. Great if storage space is limited, for occasional commutes on uncrowded trains or for chucking in he boot of the car for weekends away.
Of the 16″ bikes, the Brompton is probably the only serious contender, and still the most compact fold, great for shorter commutes but not the best choice for longer rides (although some people do mental tours on them!).
Personally I don’t really get the point of the full size folders like the Airnimal or the 26″ Dahons other than as a handy loophole to get a bike onto a train at peak times. Most need you to remove bits anyway to get a proper fold, and even if not, the resulting package is far from compact. The disadvantages seem to outweigh the advantages and to me it’s just as easy to take a front wheel off a full size bike.