When creating apps for Apple’s platforms, Swift is obviously first choice, Objective-C near second (more so if you have pre-existing code), and maybe Objective-C++ if you need it. Thanks to recent ABI stability (and inclusion of runtime libraries in the operating systems), there’s little reason not to use Swift for new apps.
But outside of the walled garden, Swift’s benefits becomes “iffy” – lack of development tools, small community, and inconclusive overall performance gains when compared with “established” languages. Have a look at this other thread reporting the experiences of developing/maintaining a server-side math-oriented app for four years and counting.