The Sky Kennel is the one you want for air travel or trips where it's essential that your animal be secure. I got the 21" for my 9.5lb cat and the 28" for my 15lb cat for traveling between the US and Germany. For daily trips to the vet, I use the smaller one. My big cat has clawed through soft-sided carriers so I only use hard plastic for him. For storage, the carriers come apart so you can store at half the size, or I like to leave them assembled and in my house as a hiding spot for my cats to use as part of their normal cat furniture. Because it's sturdy plastic, they can sit on top or go inside. I cover the top with a blanket to make it softer and so it looks better in my home.