We currently use TypeScript at work. Previously we used Flow (JS) but it was sometimes really difficult to make the types work the way you want. Especially non-trivial types were problematic. And the IDE support wasn't good, Flow took too much resources and sometimes remain stuck and do not show errors (I use Visual Studio Code). With TypeScript we almost do not have these problems. IDE support is superb, working with types is much easier and typing system seems more mature and powerful. There are some downsides (like partion inheritance etc.), but TS team is still pushing it forward. So for me TypeScript is clear winner.
I use TypeScript because:
- incredible developer tooling and community support
- actively developed and supported by Microsoft (yes, I like Microsoft) ;)
- easier to make sense of a TS codebase because the annotations provide so much more context than plain JS
- refactors become easier (VSCode has superb support for TS)
I've switched back and forth between TS and Flow and decided a year ago to abandon Flow completely in favor of TS. I don't want to bash Flow, however, my main grievances are very poor tooling (editor integration leaves much to be desired), a slower release cycle, and subpar docs and community support.