Both Can be used as Carry on, on International flights ONLY to the best of my knowledge. You can't use them as carry on, on a domestic flight. The warwagon must be collapsed also for carry on. There are size restrictions and when it's expanded it is to large. The AP Rolling bag is better suited as a carry on. From what I can gather they seem to have similar capaicity in the lower compartments.
Personally I would go for the AP bag, since you can add/remove bags on the front, giving you more flexability.
I have found that compressing the warwagon creates a lot of bulk and due to it's design it is very heavy.