We haven't really had the chance to use ours yet, since baby isn't due for another 12 weeks, but we really like our Joovy so far. DS at three still fits comfortably in the front seat and the seat back actually comes up to the lower part of his head. He also loves the jump seat and the stand on platform. We went with this one because it is lighter, shorter and folds up smaller to fit in our trunk. We have no problem getting it into our elantra trunk with the child snack bar attached. Not sure about with the infant seat adapter...haven't tried that yet. We also liked it because it came in red, which is a perfect match to the ss1 we are getting at target in the next few months.
Taking it with just DS, it seems to steer well and is easy to put together. It also fits the SS1 very securely on top with the included belt. (with all sit and stand stroller, you will have to use the infant seat for a child who cannot sit up unassisted.) I can't tell you much else, since we really haven't had a chance to use it, but I am very excited about it.