What is the best Windows Updates Strategy for servers and for clients by SCCM Automatic Deployment Rules ?

Firstly, it should be depending on your organization needs.

But in general, you may be in need to make a deployment rule one for your servers and one for your clients.

you should consider the restart for your servers, because some updates needs that.

you should focus on security patches and hotfixes, service packs.

Finally , that reply is through my experience with SCCM. I am not expert but has an intermediate experience.

ADR (Automatic Deployment Rule) for patching servers should be used as a test to specific DEV or QA servers.  Since most of the time, Windows Server reboots after update (patch) installation, using ADR for servers might NOT be a good practice for production servers.  Also, update (Patch) installation can change server application behavior causing technical unwanted issues and might cause server application from working successfully.  Therefore, it is recommended to deploy security updates to server in multiple phases (collections), review the results and so on.

On the other hand, using SCCM2012 built-in ADR objects for SCEP - System Center Endpoint Protection is mostly recommended because you don't need to review, assess and approve signature defination files for SCEP.