I had the same dilemma one year ago when Angular 2 was in RC for such a long period and i went with ReactJS. Before this switch Angular 1.x was my go-to tool for almost 4 years. To be honest i played a little with Angular 2 and i could bind the pieces quite fast because of my previous experience but i found myself struggling with TypeScript most of the time instead of Angular 2 itself.
Today with ReactJS i can use TypeScript or just Babel or Flow for typechecking or stick to its native PropTypes system for sth simpler or even skip all these in order to build sth really fast. I like this freedom and all this power in my hands.
ReactJS is much much easier since it is just the view layer. Its learning curve is really short and you can build a prototype in a matter of hours even if you are a fresher. If you need to implement more advanced stuff like sending asynchronous requests you can use the 3rd party tool you prefer like axios, fetch, superagent or whatever. As i said above, i like this kind of flexibility a lot.
I have used also Polymer for 6 months and i can tell that ReactJS is much closer to the Web Components concept despite the fact that it doesn't use Web Components technologies such as Shadow DOM etc With ReactJS we can build easily abstracted components with specific markup, logic and styling and reuse them at will.
The more you use ReactJS the more you become a better JavaScript developer. This is the ultimate feature of ReactJS since you don't have to do react-ish things. I have used EmberJS for 1 year and i remember myself searching for hours in the docs to find what objects i should extend here and there even after 6 months. With ReactJS this is definitely not the case. You just have to use plain JS features and you will stay closer to JS evolution which is extremely rapid these days. For example you can use features which are still in early stages like properties initializer syntax in ES6 classes through Babel and this can benefit you a lot as a JS developer.
I have also written an article about ReactJS here medium.com/@fakiolinho/12-reasons-why-reactjs-has… where you can read even more and i think it might help you a lot.
My advice is use the tool that is going to make you stronger and is going to serve you well. With ReactJS you 'll stay much closer to the bone and this is really important with all this frontend craziness around us. When you feel ready you can simply decide to make the next step and integrate Flow or TypeScript etc in your projects. ReactJS plays well with all of these extensions so sky is the limit.
Thanks for reading.