Depends what you want the app to do.
There are literally millions of applications available in Google Play that can satisfy nearly all your needs.
There are some great pieces of software, and some awful ones.
If you are interested, I had prepared a 2-part hub guide on some Android apps I (personally) have loved. I reckon that you will find in there some applications you will like, but I cannot guarantee you will find the 'best" app for an Android.
This is the first part of the guide, do not miss to check the second one: