We are currently on JSM Server and are very happy with it. So moving to Cloud or Data Center would be a huge disruption.
In terms of any possible move to Cloud: A must have feature for our company is the ability to have our own custom domain – we currently use support.ourdomain.com (for JSM) and kb.ourdomain.com (for Confluence).
To even consider a move to cloud, we would need this.
When will this feature be available in Cloud?
Note that anything like our.support.atlassian.net does not qualify!!!