In theory Flow has a stronger inference engine than TypeScript, which means it's more suited to incremental adoption.

TypeScript is based on an AST; which means it's inferences are limited. For example it requires you to type the parameters to a function. If the return type is derived from untyped parameters then TypeScript falls back to typing the return type as 'any'.

Flow maps the flow (hence the name) of types throughout an application, which means that it can derive the signature of a function based on the types that are passed into it. That should mean that it's a little easier to add to an existing project.

Here's an example of Flow finding an error without any type annotations: https://flow.org/try/#0PTAEAEDMBsHsHcBQBjWA7AzgF1AQwCb4BMoAv...

And TypeScript missing the same error: http://www.typescriptlang.org/play/#src=const%20add2%20%3D%2....