I didn't mention schools because you mentioned no kids, but SC is usually ranked about 48th out of the 50 states. AL and Miss. are usually lower. That said, I can say from personal experience both as a former spec. ed. teacher and a parent, school districts are very much hit or miss. I taught in an upstate district that I would never, ever, even if I had to remortgage the house to pay for private school, put my kids in. I lived in the very next district and it was much, much better. It all depends on where you buy/rent.
Crime in downtown Columbia is high compared to the surrounding area's. Compared to Newark, Trenton, Asbury Park, etc, here in NJ, it's not so bad. All depends on what you're used to. On base I don't remember it being a big problem but I never lived on base. McEntire is about 40 min away and has no housing. Most people there lived about 20-30 min away, in rural areas, and had no problems that I can recall. If I can get a DSN line in the next few days I'll call down to McENtire and see what they say.
Hope this helps.