I've recently started using Flow alongside Nuclide IDE (a Facebook-developed suite of Atom extensions), which allows me to easily see the type of a given variable.
What's nice is how much types can be inferred from just a handle of type annotations. My editor can start pointing out potential bugs at the cost of relatively little effort on my part, and that's a good place to be.
How are you finding Nuclide? When I tried it a few months ago it seemed pretty slow and unstable, and eventually ended up consistently using all my CPU after a while. There wasn't a great deal of documentation/help setting it up available (true of Flow as well to a lesser extent), which was why I chose TS at the time, but am definitely interested in seeing how Flow is progressing.
What's nice is how much types can be inferred from just a handle of type annotations. My editor can start pointing out potential bugs at the cost of relatively little effort on my part, and that's a good place to be.