I've only owned a couple (Bike Friday and Giant). Of those the Bike Friday wins by leaps and bounds. Giant was my first folding bike... I learned from that what I definitely didn't want in a folding bike.
I've test-ridden a few more (Birdy, Dahon, Brompton). Of those, I thought the Birdy gave the best ride. The Dahons weren't slouches. The Brompton gave a bouncier ride than I expected. For the breadth of options available, Dahon is the winner here, even though Birdy was really nice. That said, I wouldn't balk at owning any of these.