Mobile App Development

Hi! I am planning on developing an application for Android and iOS and wanted to know which programming language or frameworks are best/most commonly used for app development.

I come from a computer engineering background so I am used to working with C/C++ and Python too.

I have heard that maybe C# or React js is good, but don't really know. I am up to learning anything new so please let me know what is the best choice. I imagine that as everything there isn't a best choice so if you could also reason your answer (pros and cons) that would be great!

Thanks! 🙂