I used Graylog until a few months ago, and I'm currently using Sentry. With Sentry it is quite easy to filter, for example, errors for a specific project just by clicking a drop down. On Graylog, we had to perform active filtering through the search bar. The filtering process was a bit different. I wouldn't say they differ too much, but Sentry also allows me to do some bug tracking and mark them like, "Okay, now I have to review this," or "This has been resolved", which is not something I would ask for in a log tool, but it's available.

Splunk, Logstash, and Elasticsearch.

I reviewed Logstash and Loggly. 

All the other solutions were in-house proposals.

Yes, we were thinking about the Logstash family, but due to similar issues with the building codes as in the Graylog Collector Sidecar case, we decided for Graylog.

Yes, Elastic Stack.

ELK was another option. However, Graylog appeared to be more robust and had less limitations at the time.

We had evaluated ELK Stack, but found Graylog more useful for our use case.

This decision was already made before I got to the organization.