Which one is better start to learn Angular 1 or Angular 2 ?

Answer 1

Angular 1.x was not built with mobile support in mind, where Angular 2 is mobile oriented. It depends on your needs

Answer 2

AngularJS (aka Angular 1) was completely restructured with Angular (aka Angular 2) and they've kept in that direction with the release of Angular 4 (not sure why they skipped 3, I skipped that piece of documentation). I recommend Angular 2 or 4 as a good place to start. angular.io is the site and v2.angular.io for Angular 2.