Community settings apply to all portlets in the current Community, and are shared by all users of that community. Generally, Community settings are set by a Community manager.
CommunityPortlet settings apply to a particular portlet, but are shared by all users of the current Community. Generally, CommunityPortlet settings are set by a Community manager.
User settings apply to one particular user, but apply to all portlets accessed by that user. The administrator must configure the portal to send User settings to a portlet.
UserInfo settings are read-only settings that are generally pulled from third party user repositories. The keys for the default UserInfo settings, such as FullName and EMail, are available in the UserInfo class.