I suggested the below 5 fonts to use to impress your visitors.
Open Sans – Google FREE font
https://fonts.google.com/specimen/Open+Sans
Roboto – Google FREE font
https://fonts.google.com/specimen/Open+Sans
Poppins – Google FREE font
https://fonts.google.com/specimen/Poppins
Nunito Sans – Google FREE font
https://fonts.google.com/specimen/Nunito+Sans
Montserrat – Google FREE font
https://fonts.google.com/specimen/Montserrat?query=Montserrat
Not just use these fonts also learn the importance of typography in mobile app design.
This will help you to keep uniform heading sub heading and paragraph font sizes.
Google in Material Design guidelines recommends setting the minimum size for Body text to be 16sp