It depends on what are your goals. You're right: Angular 1 and 2 are two completely different beasts. I think Angular 2 will be the future, but Angular 1 is here to stay for some time as well. Honestly, you won't like my answer, but I think you should learn them both, in order to be able to collaborate on already started Angular 1 code, and to start new projects in Angular 2 as well.
As for React, I don't know: it surely is really popular, but my impression is that most of its popuplarity comes from being really different from Angular 1, while it's a lot more similar to Angular 2 (but providing only the view rendering engine).