If you've got a critical app, which is supposed to have a zero error rate, and you'd like to get notified in real time, every time an error occurs, Exceptional.io is for you. You can configure notifications via the web Dashboard to be notified via SMS at the exact time an error occurs.
Like all the other error tracking applications, Exceptional.io also offers a good user interface with a vast list of powerful functionalities namely: intelligent error grouping, view backtraces, filter by recency, capture custom data, etc.
If you have a mobile app built using web technologies, you'd require a bit more than just an error pin pointed in your JS file or even a stack trace. You'd want yourself to be notified of the OS versions the errors are frequently occuring on, and a little more client side data. And BugSense
Even though it might seem ironic, but one of Bugsense's pros is also one of its cons. The free plan is limited to only 500 crashes a month, and has a pretty tight limit on the size of the APK (Android) you can integrate it with.
Airbrake.io boasts a beautiful user interface which gives easy access to features such as intelligent error grouping and application insights, session details and backtraces. All these allow you to squash those bugs at a much faster pace.
By including Airbrake's client side error tracking JS into your code, you won't have to worry about it affecting your page load times at all. Since the library loads asynchronously, which means it won't cause painful delays for your site's visitors.
Airbrake is non-free software, so it cannot be self-hosted, audited, or improved upon by the community. Your data is insecure - open to be read by Airbrake Inc, and if they shut down you will be unable to continue using the software.