Based on a quick play recently, I'd say still slightly wonky. Nuclide has improved a lot but autocomplete etc. is noticeably sluggish compared to the atom-types

Based on a quick play recently, I'd say still slightly wonky. Nuclide has improved a lot but autocomplete etc. is noticeably sluggish compared to the atom-typescript plugin. On my travel 12" Macbook, Atom with Nuclide it's too slow to comfortably use and the Sublime plugin for Flow seems to be quite buggy, whereas the Sublime TS plugin is pretty solid. In terms of type definitions available for third party libraries, Typescript is way ahead. I also think the documentation and community around Typescript is stronger, and will only get more so with the move to use TS as the default in Angular 2. Also the stability is great and the roadmap looks promising. Nothing against Flow, I think it is great and definitely has some advantages (and anything which adds types to JS is a winner in my book!), but it feels slightly more like an internal Facebook tool that happens to be released to the public versus Typescript, which is more of a release quality product. But yeah, either is great improvement over plain JS and I'd definitely consider Flow for a personal project, but in a bigger company/team environment I think the stability, tooling and community of Typescript would make me push for that.