I really do love the Parkway, but a few things I like more about the Vivo: it doesn't seem as tippy. The Parkway tips on corners in all the vehicles I've used it in (some worse than others). I've never driven with a Vivo in my car, but just based on playing with it in the store, sitting dd in it, buckling her in on the test bench, the Vivo does not seem as tippy. The Vivo seems wider at the back of the seating area, and the Parkway gets narrower at the back. Slim kids might not have a problem with that, but some kids feel like they have to sort of "wedge" themselves into the Parkway. The Vivo positions the lapbelt lower on the actual lap/upper thighs rather than the hips/lower abdomen. I prefer this positioning, but the Parkway's lapbelt positioning isn't
bad, either. The Vivo seems to sit lower on the vehicle seat, as well (I'm going to go dig up my booster comparison photos to illustrate this point, and the lapbelt positioning). I like carseats that sit lower on the seat, blocking less of my view, easier for the child to climb into by themselves.
ETA: Nevermind, I see that Teri posted my link earlier in this thread.
Look over those pics to see what I mean.