The Softpak is just slightly bigger. For air travel the Cabine is best, lighter and smaller, plus it can be worn as a backpack.
Overall I still prefer the Softpak though for 2 reasons:
1- the storage compartment under the sax has a hard lid that prevents small items from moving around, while on the Cabine it's open. I only store a swab and neck strap in the Cabine while in the Softpak I carry those items plus a reed case, cork grease, extra individual reeds, mouthpiece swap, cleaning cloth. all well secured under the lid, under the horn. neck and mouthpiece in the bell in both cases.
2- although I prefer latches over zipper, I find the BAM latches on the Cabine too easy to open by accident. they have a protruding lip that tends to catch on things and easily open. when traveling I always lock the latches with the key that comes with it. I've had my Softpak for a couple years now with no issues with the zipper.