You're right in that we don't have those choices. But out of that group, I'd maybe take Orton and Cousins. Not sure why you really think Nassib is that good. Maybe he is but he had something like a 60% completion rate playing in THE worst conference in major college football. Matt Moore has real issues between the ears unless he changed something from his college days and early pro career. Jason Campbell? I don't think he gives us a big advantage over KC even if he knew the offense. And Shaun Hill may be a little better but practically IS Kellen Clemens - a career back-up for a reason. I fail to see any future upside with any of these guys besides Cousins - who we are not getting away from WA, and maybe Nassib because he might - MIGHT have upside in the NFL. If we're going by college numbers, KC's college numbers far outshined Nassib's while playing in a much better conference.
Anyway, Kellen will likely never impress us as a true #1 QB but given the real choices that we ACTUALLY do have, I'd keep him even over most of those AND the options on your list.