I've owned a Curl for a bit now. I rode a rental Brompton on a bike+train tour in Scotland (oh, what fun!).

So, yeah, conventional wisdom says the Brompton, with a rudimentary suspension and a relatively smaller section steel frame and handlepost, rides smoother, and the Dahon, a hardtail with larger section aluminum frame and handlepost, is more efficient. Shrug. Riding the bikes weeks apart on different continents, I have no memory of any meaningful difference along those lines.

I'm more comfortable on my Curl than I was on the Brompton only because I've adjusted the Curl to fit me, and I just got what I could rent with that Brompton. If I owned a Brompton, I could use my favorite saddle and get the handlebar height just right.