Most Common: TypeScript
ES5 is fully supported. Angular can be used without using any new or future JavaScript language features.
ES6 is fully supported. With that being said, the community typically recommends switching to TypeScript if you've moved beyond ES5.
Angular is TypeScript focused and is the recommended language for development. Most docs and examples online are and will continue to be written in TypeScript.
Using flow with angular is not a common practice. If type safety is desired, the community typically recommends TypeScript.
There is no official support for JSX in angular. There is a few community libraries that attempt to bring support to angular but they are not widely used or maintained.