In this particular Draft if he came out, Matt Barkley and Ryan Tannehill would have been in a tough battle for draft position. I think Matt Barkley could have won that battle, but it's all very team specific so you really don't know. I said before he stayed in school that this process was set to be unkind to a JUNIOR Matt Barkley, because he wouldn't get the opportunity to show his stuff at any All Star games, and every time he suited up at Combine and pro day settings the teams would be reminded that he's not big or physically imposing, and doesn't have an elite natural arm. But then, with Tannehill breaking his foot, he also did not have the opportunity to show anything...so that's a tough call. If Cleveland passed on QBs at #4 because they liked Weeden at #22...then Tannehill might have gone above Barkley just because of all the stuff Miami had in place at #8 overall that made Tannehill the guy, between Philbin and Sherman.
I don't believe Landry Jones would have been in the same mix as those two. He's a talented prospect and he would have probably dusted the second tier of competition after Weeden (we're talking Osweiler, Wilson, Cousins, etc). However, I think comparisons between Tannehill and Jones would have been easy for teams to decide because Tannehill has the better pocket presence and better mobility. Those would have been the deciding factors.