Nobody is a sure thing at certain points guys like Robert Gallery, Aaron Curry, Glen Dorsey were considered sure things. Outside of Andrew Luck I can't think of one QB who was considered can't miss.
I'd love the Bills to take Manziel, I don't think it'll happen. If a team is trading up to the top pick for anything other than a QB, Whaley has to go. Clowney would have to be better than Bruce Smith to justify the trade.
With that said Ramses Barden is the guy the Bills should bank on?