There's alot of stories about where Federal XM193 comes from. Search the forums and you'll find plenty.
Relatively speaking, the SA is slower burning and not as hot with smaller flash than Federal XM193. Accuracy seems about the same. I've not had any malfunctions from XM193, but I've had a few with SA having shot much less. The SA is much older, and the storage on the SA wasn't perfect, but it hasn't suffered much for it. One real difference is that SA has an ammonia smell to it when fired that's hard to miss.
I wouldn't say one is much better than the other. It probably has more to due with luck of the lot you get than anything else. I shot about 100 rounds SA and 200 rounds XM193 today alternating and they worked fine.
SA is occasionally priced very attractively relative to XM193.