Geno Smith is a solid prospect, he's not a slam-dunk #1 but he's good. He might end up being as good as Wilson, except he has more size. He's not as fast as Wilson though.
Landry Jones is trash. He piles up stats against bad teams and lays down when his team needs him most. He's also a statue in the pocket, and literally crumbles under pressure, both the pressure of big games and the pressure of the pass rush.
Matt Barkley is a joke, just like virtually every other USC QB. He, like Sanchez and Leinart, do not have the physical ability to play the position, and unlike guys like Chad Pennington (if he had an average arm he'd be a HoFer, sadly there are probably several people on Smogon who have better arm strength), they don't make up for it with HOF-caliber ball placement, intelligence and savvy. Matt Barkley has not thrown a deep pass in his career that he hasn't made his WR have to fight to go up and get. I've never truly seen him hit a WR in stride, certainly not under pressure.
Look at how RGIII, Wilson and Luck threw deep last year. Hell, look at Cousins or Weeden throwing deep passes. MILES ahead of Barkley. Miles. Even Tannehill threw deep better than Barkley.
Barkley will get drafted high because he's perceived to have good intangibles, he put up good numbers throwing to top 16 NFL WRs and protected by NFL offensive linemen, and he gets USC hype.
Tyler Wilson is probably the 2nd best prospect and he needs to go back to school.
I'd burn a 3rd rounder on Logan Thomas because he has a unique physical skillset but I have a feeling he's gonna be the next Tebow, which wouldn't be a bad thing if he accepts being a gimmick player (assuming he doesn't develop, Thomas's throwing motion isn't broken like Tebow's is, he's just super raw)