Never overrides everything - so even if there is an explicit "Allow" somewhere it will still resolve to a deny.
Revoke will revoke the permission from a user permission or user group permission but it can be overridden by an explicit "Allow" somewhere in the node permission.
For example:
Node 1:
View Node:
Registered: Revoke
Administrative: Allow
Result: Anyone in the Registered user group can't view. Anyone who is in Registered but also in Administrative can view.
Node 2:
View Node:
Registered: Never
Administrative: Allow
Result: Anyone in the Registered user group, regardless of their other user groups, cannot view. The "Never" explicitly overrides any other permission.