I own two jackets. I don't believe the pockets are unusually big, nor did I buy the jackets with them in mind, yet the mini slips into them comfortably. It goes with me everywhere. In addition, it's small enough I can hold it effortlessly in one hand while using the other to copy down problems from it on the blackboard for the classes I teach.
Obviously, the larger screen of the Air is nice, and for some people that's going to be more important than the convenience of the smaller size. Different people will use the devices in different ways and have different priorities, and therefore different trade-offs will be appropriate for different people. Given the way I use it and the priorities I have, the Ipad mini is the perfect size: any smaller and it would no longer be comfortable for reading, while any bigger and it would no longer be so extraordinarily portable. But I would never say it was somehow objectively best for everybody, that would be silly.