I don't currently ride a folder, but for years I used to keep one in my car boot and use it regularly for an hour or two (while waiting for the kids to finish football training/ brownies / swimming or whatever). The four folders I've experience of are:
Brompton - just didn't feel big enough, even with the extended seat-post (I'm 6'2").
Dahon Speed-Pro - worked very well, but did feel flexy compared to a normal bike.
Giant Half Way - my main reason for posting as this bike seems to get overlooked. A very good bike IMO. It is flexy, but not as much as the Dahon. It's big enough for tall-ish people with no alterations and it looks funky
(single sided swing-arm and fork). Spec is basic but adequate. It doesn't fold as small as the others.
Birdy Green - limited experience of this, but I just couldn't get used to the back pedal brake (tho' that may be a peculiarity of the particular model I had?)
I didn't use any of the bikes as commuters, or take them on public transport. As long as they folded small enough to fit comfortably in a car boot that was enough for me. Everything I've read suggests that the Brompton is by far the smallest (and neatest) folded if that's important to you.