Which of the 3 phones is best? Huawei p20 lite, Huawei mate 10 lite or Samsung a6?

I mainly use social media, listen to music and need a not too bad camera.

Does anyone know that and could advise me which would be most suitable?

Since you want a good camera, I would take the P20. Social media and music can all mobile phones, because you do not need a certain / good performance and the phone is also in terms of performance quite good up there.