I am an Android Developer, I have been developing Android apps for a long time, but now I am asked in the company to start developing hybrid mobile applications with Ionic.
As I always do, I searched in Udemy and picked the top-rated courses in Angular2 and Ionic2 because the instructor of the Ionic course said that Angular 2 is a prerequisite for Ionic (given that I know HTML, CSS, Javascript), but I found that the Ionic documentation says I should learn AngularJs. Another thing that made me more confused is that in Udemy most of the courses teach Ionic with Angular 2 or 4 and only very few take the AngularJs Approach and even those few lack the quality available in the Angular Courses.
Ionic framework is just an UI framework for the hybrid mobile apps, it uses AngularJs/Angular as core framework,
Ionic v1 uses AngularJs and Ionic v2+ uses Angular v2+,
an example for that if your are using the latest Ionic v3+ you will find the core functionality is in Angular v5.2+.
I recommend to use Angular v2+ with Ionic v2+ because it's the future of the web/hybrid technology. you will find yourself learning ES6, Typscript out of the box when you are using Angular v2+.
You can start with this tow courses:
https://www.udemy.com/the-complete-guide-to-angular-2/learn/v4/overview
https://www.udemy.com/ionic-2-the-practical-guide-to-building-ios-android-apps/learn/v4/overview
Hope I make things a little clearer.