Both are similar in that they are component-oriented.
There are two important factors in my mind.
1. The ecosystem (as you mentioned). React has a clear head start here, but I expect Angular2 to make some gains over time.
2. Angular2 gives you a full framework, and as they say now, a whole platform. React is smaller and you rely on a bunch of other packages to get all the extra features you need. If you want a full solution, Angular2 gives you that.
This can be argued as a good thing or a bad thing. More flexibility with React, but also more things you need to figure out and make a decision about. With Angular2, once you buy in, you don't need to make all of those decisions.
In my particular circumstance, which is to migrate an Angular1 app to a newer framework over time (mainly for the server side rendering features), Angular2 provides a clearer path and offers some nifty features like component styles that allow a similar migration with CSS.