The above sounds negative but TS is still the best bet right now imo. Some people will prefer Elm or Purescript for better type systems but I like staying close to JS.
With regards to types: TypeScript has only recently added support for any kind of Algebraic Data Types whereas Flow was built upon Unions and Intersections from day one. That to me speaks to their priorities.
https://blogs.msdn.microsoft.com/typescript/2015/01/16/annou...
https://blogs.msdn.microsoft.com/typescript/2015/09/16/annou...
They seem to be moving at a decent, agile pace to improving/expanding upon the algebraic sides of the type system.
Thank you for correcting me.
(It will be opt-in as Typescript follows a rule of increasing strictness via compile options to support the spectrum of JS needs, but also as it will not be entirely backward compatible with existing type definition files and will need some effort among typings authors.)
I prefer the idea of Flow as well but tooling and community is not there yet
The fact that last time I checked, it wasn't able to consume TSD signatures from third-party libraries (or offer an equivalent system with a significant amount of libraries) is a much bigger issue IMHO.
When I bring up the latest and greatest (eg. Flow) it doesn't actually work on Windows because Windows is as I see it an after-thought for a lot of the Open Source world.
But I've brought up this exact problem (the lag in tooling) to .Net/Windows devs before and they've told me I'm wrong and that they've got all the latest and greatest dev tooling like everyone else.