Here in Illinois both species are good for posts/firewood, the best.
I'd guess both will grow in Georgia but I'll defer that to someone from
that region. Osage Orange can be used as a post green, but Black Locust
should be let dry about a year before putting it in the ground to be on
the safe side. Generally, it's my understanding that Osage Orange will
outlast Black Locust slightly; but at 50+ years, who's going to
complain? My preference would be Black Locust as it grows fast and
straight. The downside of it is that it will spread in full sunlight
conditions. Here it seems Black Locust prefers drier sites whereas Osage
Orange will tolerate wetter sites. Good Luck!