I've been using both Bugsnag and Sentry for years and I would recommend both of them and as Tom Maiaroto mentioned "they are roughly the same". Bugzilla is a different kind of animal, that is more of an issue tracker like Jira or Redmine.

Despite what Tom Maiaroto wrote, we're using these tools more for the backend and less for the frontend, so I am going to give a brief insight into how we use them in our Telemetry stack for monitoring the backend.

Sentry and Bugsnag are advertising themselves as Application Monitoring, but their definite focus is on Error Monitoring. This is what they originally were made for and this is were they shine.

A typical confusion is that we think they are mutually replaceable with APM tools like NewRelic's or Datadog's APM. Albeit both are doing very similar things, there are several significant differences:

• NewRelic/Datadog APMs are sampling exceptions, so you don't have a "complete catalog" of your errors
• Sentry and Bugsnag are collecting very detailed data (stack trace, HTTP request, user, device, host, etc) of each exception, thus you'll exactly know when, where, how many times and to whom those errors have happened.

The focus of those APMs is broader and can give you a much bigger picture like distributed tracing, logs, processes on the hosts at the given moment just to name a few. But they are not designed to give you a laser focus on each specific error.

So the bottom line is that they are complementing each other.

Sentry is more affordable especially if you have more than 5 users. I personally prefer Bugsnag because of the cleaner UI. But at the end of the day, they're both very valuable and lovely gadgets in our toolbox and help us a lot being on top of our systems