My understanding is that if you check/uncheck Contact record Field 'Email Opt out (HasOptedOutOfEmail)' field in salesforce then the record/contact gets updated in Marketing Cloud.
But for some reason it is not updated or maybe it doesn't do anything at all.
So what is best way to update All Subscriber List for Unsubscription/Subscription?
In my experience, the only way to achieve this globally (and without code) is to use the unsubscribe/resubscribe custom links. It sounds like you are already using this (included with the Installed Package). Even if you resubscribe the contact in Marketing Cloud, it will not share the update with the Email Opt Out field in Salesforce.
SELECT * FROM _Subscribers WHERE EXISTS (SELECT 1 FROM DataExtension WHERE _Subscribers.EmailAddress = DataExtension.EmailAddress)
This should give you everyone from the Subscribers Data View who matches on your uploaded Data Extension on the email address, and will now also give you the Subscriber Key for these people, as well as their status.
Export this newly populated data extension
Open it up in Excel, change all the Status values to Unsubscribe or whatever you want to do with them.
Best Answer
You need to add the link "Marketing Cloud Unsubscribe" to your page layout in Sales/Service Cloud in order to get the status to synchronize correctly. This would be the best option to do update the status from Sales/Service Cloud. You can find this link in "Custom Links -> ExactTarget Unsubscribe" along with the Resubscribe link when editing the contact/account page layout. Other ways include doing this directly in Email Studio or via the Marketing Cloud API.
Further information can be found in the documentation about Marketing Cloud Connect - Unsubscribes.