How would you compare Dragonfly to Fox 3?
The main difference between the two (I mean, there are many design differences, but functionality-wise) is that the Dragonfly is a smaller model. It is much lighter and much more compact. That means = much less all-terrain features, a less sturdy frame, a narrower (smaller) seat a bit, and smaller wheels (more getting stuck in holes). And also, the lie-flat (non-bucket) seat of the Dragonfly which is a feature some missed a lot in the FOx.
Personally, I think the Fox 3 is still the better all-rounder and the more versatile stroller. The Dragonfly is an option for those urban moms that mainly struggle with stroller's size and weight and need something as small and light as possible while still trying to remain a full-featured model. I do like the Dragonfly idea and design, however, I feel the Cybex Mios does a similar, if not, in some ways, a better job, and for a more all-round model, the Fox would be my go-to (considering, though, the larger fold is not a no-go for you).