Should I use typescript? or I can just use ES6?
I've been using Typescript in my current angular project for about a year and a half and while there are a few issues with definitions every now and then the DefinitelyTyped project does an amazing job at keeping up with the latest versions of most popular libraries.
Having said that there is a definite learning curve when transitioning from vanilla JavaScript to TS and you should take into account the ability of you and your team to make that transition. Also if you are going to be using angular 1.x most of the examples you will find online will require you to translate them from JS to TS and overall there are not a lot of resources on using TS and angular 1.x together right now.
If you plan on using angular 2 there are a lot of examples using TS and I think the team will continue to provide most of the documentation in TS, but you certainly don't have to use TS to use angular 2.
ES6 does have some nice features and I personally plan on getting more familiar with it but I would not consider it a production-ready language at this point. Mainly due to a lack of support by current browsers. Of course, you can write your code in ES6 and use a transpiler to get it to ES5, which seems to be the popular thing to do right now.
Overall I think the answer would come down to what you and your team are comfortable learning. I personally think both TS and ES6 will have good support and long futures, I prefer TS though because you tend to get language features quicker and right now the tooling support (in my opinion) is a little better.
Decision tree between ES5, ES6 and TypeScript
Do you mind having a build step?
- Yes - Use ES5
- No - keep going
Do you want to use types?
- Yes - Use TypeScript
- No - Use ES6
More Details
ES5 is the JavaScript you know and use in the browser today it is what it is and does not require a build step to transform it into something that will run in today's browsers
ES6 (also called ES2015) is the next iteration of JavaScript, but it does not run in today's browsers. There are quite a few transpilers that will export ES5 for running in browsers. It is still a dynamic (read: untyped) language.
TypeScript provides an optional typing system while pulling in features from future versions of JavaScript (ES6 and ES7).
Note: a lot of the transpilers out there (i.e. babel, TypeScript) will allow you to use features from future versions of JavaScript today and exporting code that will still run in today's browsers.