I went to NPTU in New York. I also live in New York State now. It is a beautiful place, but it snows tons. If you're going to be there in the summer, I'd pick NY because Charleston can get pretty hot and sticky that time of year. You'll get enough of that inside the plant.
Secondly, I understand that the Charleston prototypes consist of a couple of decommisioned boomers with S3G/S5W power units. Since those are all but a memory in the fleet, I would rather learn on something that is a little closer to the current technology. S8G is as close as it gets, and that is a quarter century old.
Whichever you get, best of luck to you.