Choosing code language when using Angular2: ES6 or TypeScript

We know that we can write angular2 web app with TypeScript, JavaScript ES6 or JavaScript ES5. Angular2 itself is written in Typescript and their documentation and tutorials shows example written in Typescript. With that in mind, does that mean that writing app in TypeScript when using Angular2 in the most preferred way?

I think ES6 should be more favored that ES5, that leave TypeScript VS ES6. What is the pros and cons for writing Angular2 app using TypeScipt and ES6?