From my experience - Flow is still very "unstable" and in heavy development. I haven't tried TypeScript at all, so I cannot compare that.
It's absolutely true that Flow team is merging all pull good requests, fixing issues (the backlog is big - 500 issues - but TypeScript has 1000, so it's not incomparable) and the system is made dramatically better every release.
But there are still rough edges, especially when working with ES6 modules and import/requires/etc.
Again, I don't know how TypeScript compares, I learned Flow and am just using that.
The good thing TypeScript has going for it is tooling. It's really solid. IMO, VSC is a pleasure, and the tools (tsc, tslint, etc) are extremely stable. Things don't break.
The GitHub community is going really fast, and I love reading some of the PRs, but it's hard for me to compare in that sense.
It's absolutely true that Flow team is merging all pull good requests, fixing issues (the backlog is big - 500 issues - but TypeScript has 1000, so it's not incomparable) and the system is made dramatically better every release.
But there are still rough edges, especially when working with ES6 modules and import/requires/etc.
Again, I don't know how TypeScript compares, I learned Flow and am just using that.