Jesus christ, all the old farts on here piping up, some are tongue in cheek but a few I suspect not as much as they'd like to pretend. I've used OzRunways a lot and it gets my vote as being quite rigorous and lots of great features to take advantage of. But as others said they all usually have a 30 day trial so I'd say give them all a fair crack and see what suits you best. If you've got MS Flight Sim at home then most of them have plugins to use them with it so can simulate some short flights to see how they hold up and get a better idea of what to expect inflight.
Also take into consideration that some have different Android vs Apple versions/features, I specifically had to buy an iPad a long time ago for OzRunways because the features it had there were above and beyond that of Android which still seems to be the case, see
this link for comparison, and would recommend checking this for other apps as well to see what you're getting and consider whether you might need to buy an iPad or Android device instead.