I don't know, Rust has Mozilla behind it, and lots of active development and (for a new programming language) a pretty decent community.
ATS is hosted on SourceForge, and looks to be someone's research project. That's totally fine, and it may actually be _better_, but the real world often doesn't care about better.
If I was a betting man, I'd be putting chips down on Rust. (and I sort of am...)
That said, the more programming languages the merrier!