Honestly, I think either one would be fine. Johnson seems to get some decent talent to come to SC, when it's been clear for a few years now, that under Spurrier, the offense is sputtering because of QB issues and the Defense was going to be relied upon to keep them in games, and it would only get tougher as the schedule got dragged on.
I think Johnson (if the buyout can be dealt with appropriately), would be a good one.
VanGorder - While it would be a pretty sweet hire to have him next to Chizik, I'd be really surprised to see him take, in what would be in my estimation, a demotion. He's a DC in the NFL now, and under Chizik, would be working alongside another DC basically. If they made him Asst HC (assuming Malzahn isn't going to be), then it COULD make sense, if VanGorder really wants back in the college game. Lord knows from his GA days, he can recruit.
So, when all is said and done, Johnson would be a good one, while not a splash hire. VanGorder would be an excellent hire, a surprising splash, and interesting story going into the remainder of recruiting season.
We shall see.