Go for the Cobalt! Size depends on what you want to use it for. I have 2 55s and really only use them as luggage for trips. They are too big for everyday use. For me. I 45 is on my wish list because I think it would be more versatile and I'd get more use out of it. My Kusama Keepall has a pocket inside of it but it's honestly kind of useless. It's flat and doesn't hold much. The only thing I really keep in it are the lock and keys. Just fyi.