On-Prem vs. Cloud?

We use both and I think each has a purpose. Some of the advantages of the on-prem server (besides cost) are that if you already use SSRS then you probably have a security model in place that you can leverage. I think it's easier for users as they only have to go to one place for their reports (depending on your setup). It works really well connecting to on-premises datasources. I like the report server branding option, and the ability to monitor report execution by querying the report server database.

Some of the drawbacks and issues we've had:

• it can be a little buggy. I got to work one day and all of our connection strings were displaying in chinese (literally) and wouldn't work. We had to restart the service. Other times we couldn't upload reports and had to restart the service.
• It doesn't have all the same features of the web service. No dashboards or QA.
• You have to use a different version of PowerBI desktop to publish to the report server, and it's a few months behind the normal version in terms of features.
• We've had issues refreshing data from online sources. E.g. OAuth2 isn't supported so we can't schedule refreshes from SharePoint online or OneDrive for business.
• Depending on your setup, you can only access the reports on-prem.

That being said, we're planning to expand our use of the on-prem server, but we still use the cloud service for any reports sourced from cloud data sources, or anything that needs to be accessed from anywhere.