For all the preflight & navigation I think most pilots use sky demon. It all depends on what your using the app for and your interests.
Im a PPL holder and I love to find new off-site landing locations to increase the accessibility of my helicopter travels. I was speaking to my mate recently and he recommended - Helipaddy. Its an app that is a must have for any UK helicopter pilot. It has mapped out a tone of landing location into a database that provides awesome information like landing information, site details, any hazards etc.
The app has only recently been released and is relatively unknown from my perception so it has been a good find.
If you Helipaddy into google you should find it. Let me know what you think
! Ive been using the app on weekends to find new locations to explore!!