Crashlytics is a mobile analytics tool which helps users find the exact line of code that their app crashed on, providing granular insight into mobile app performance and user experience. Crashlytics was acquired by Google in 2017 and is now offered as part of the Firebase product.
Firebase Crashlytics is a no-brainer if you are already using any of the other Firebase suite of products, as its integration is very easy if you are already using these in your app. If you have cross-platform Android, iOS, and macOS apps, you should also consider Firebase Crashlytics to provide a unified across your platforms. If your app is only on Android or only on Apple, then you may be better off remaining with the default Apple Developer or Google Play Developer Console crash collection experiences.
It is very easy for non-developer staff to use the Firebase Console and gather information for the development team. Developers will find it straightforward to integrate Firebase Crashlytics into new or existing codebases using Google's in-depth developer documentation. I cannot think of an easier cross-platform solution to use, and because of that I wish it supported more platforms!
Compared it with Crittercism on a Xamarin project a while back and on that platform, Crittercism was the best. But on Android, Crashlytics is just a lot better in providing good stack traces and having a useful analytics console. It's pretty much the defacto standard on Android...everyone uses Crashlytics. It's even more common to use Crashlytics and the Firebase crash tracking; Firebase does track ANR's a lot better though.