When comparing Bugsnag vs ErrLytics, the Slant community recommends ErrLytics for most people. In the question“What are the best JavaScript client-side error logging services?” ErrLytics is ranked 6th while Bugsnag is ranked 7th. The most important reason people chose ErrLytics is:
It's very easy to integrate and tracks every user events, you get real-time updates. A must-have tool on your site to track down bugs and make the user experience better.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Great documentation
Clear, concise documentation. Plus docs on cross-domain script errors and enabling CORS.
Pro Email, chat, sms notifications
Bugsnag can be set up to send email notifications as soon as exceptions occur. It can also integrate with a number of third-party services that can be used for notifications including Campfire, HipChat, Twilio SMS and custom solutions via Webhook.
Pro Automatic issues/ticket creation
Bugsnag integrates with a wide variety of 3rd party tools to automatically create issues or tickets. Integrations include GitHub, BitBucket, UserVoice, Trello and many, many others.

Pro Has a free plan
After a two-week full-featured free trial period the user is limited to 2,000 errors/month, 1 user and 1 project.
Pro Exceptions are grouped
Bugsnag groups similar exceptions together displaying the number of occurences so that there's no need to deal with each instance of the error separately.
Pro Exceptional documentation organization
Their documentation was well organized, easy to search through for the platform of choice and quick work of full product integration.
Pro Supports Unity 3D
Drop in place integration with Unity 3D, only a simple API Token configuration on game object and everything was up & running with almost zero code written.
Pro Supports phabricator integrations
Not many products have decided to finally start doing this, phabricator now has a champion.

Pro Source map support

Pro Stack traces
Pro Client libraries are open source

Pro Report uncaught errors
Pro Good web UI
Pro Integrations
It's very easy to integrate and tracks every user events, you get real-time updates. A must-have tool on your site to track down bugs and make the user experience better.
Pro AJAX errors
Helps you know when the API call is failing so that you can quicky get to it.
Pro Event telemetry to reproduce error
Records action that led to the error which makes it easy to reproduce the error faster. Events recorded are console logs, network calls, route changes and user events, like clicks and inputs.
Pro Network performance monitoring
AJAX monitoring shows which calls are running slow and how many calls the app is making to the backend. Also, provides data transfer reports and throughput reports.
Pro Notifications
Allows integrating various notification channels like Slack, Hipchat & Email. Notifies whenever there's a new error or a resolved error appears again.
Pro Page load performance monitoring
Monitors page load performance along with the breakdown like Query stalling, SSL, TCP Handshake etc. It also provides in-depth monitoring, including duration filtering, URL filtering and AJAX calls made from the page.
Pro Drag & drop source map support
It's really easy to debug minify code. Source map support, not just beautifies the code, but also fetches code context.
Pro Daily error reports
Daily reports help understand anomalies that triggers errors. Also, gives top erroneous browsers, URLs etc within the report.
Pro There's a free plan
ErrLytics provides a free plan which helps to monitor small-scale websites, a feature that is mostly absent in other services.
Cons

Con Blocked by ad blockers by default
Bugsnag is blocked by the AdBlock EasyPrivacy filter.