I gotta go Royalty here.  Prince is the pick.  That would allow them to address safety by moving one of the current corners if they wished.  He is a top flight Cb, which they have needed.  Too good a value.
 
As for trading, the ONLY way I see a trade by Dallas is if one of the top two Qbs falls.  If Gabbert or Cam are there, they could get some serious value to trade down with Minny.