The Fractal Design case is an ITX case while Corsair Air 240 can support mATX and ITX. If the number of expansion slot is not your concern, go with whatever your budget allows you to. Personally, I would choose Corsair Air 240 because of it looks. The thing is, I had Corsair 240 in my mind for my build but later went with Corsair 400C because the former couldn't accommodate MSI Gaming X RX 480.