Locker may not have done himself any favors by staying an extra year financially, but it may have been a good move by giving him the opportunity to be on a good team. Also he did whichever NFL team drafts him a favor by killing his draft stock. If he does pan out, I'm not convinced either way, some team will have gotten him for a steal.
As to the original question, I'm not really sure who the Panthers should take. What other needs do they have? I know this is going to sound crazy on an NFL fantasy site, but I don't really follow the NFL closely enough to know.
If they want a big talented receiver they could go for AJ Green out of Georgia or Julio Jones out of Alabama. If they want to improve their pass rush, which they should, they could draft Da'Quan Bowers out of Clemson, Nick Fairley out of Auburn, or Stephen Paea out of Oregon State. All are big athletic DE/DT's who I think will shine at the next level.
The big 3 as far as QB's are Andrew Luck-Stanford, Ryan Mallet-Arkansas, and Jake Locker-Washington. Cam Newton should also garner a look although I'm not completely sold on him. If they go QB it has to be Luck, although I think Mallett is going to surprise a lot of people.