BaseComponentModel, BaseElementModel and BaseEntryRevisionModel all ultimately end up extending BaseModel, which itself extends Yii's CModel.
I like to think of them, roughly, as beefed up Data Transfer Objects. Primarily useful for transferring data throughout the various layers of Craft (templates, controllers, services, etc.).
Regarding which ones you extend, it depends entirely on what you are trying to do in your plugin and with your Models.
BaseModel is the most "generic" one as far as Craft is concerned that gives you all of the Craft specific attributes of Models.
BaseElementModel is useful if your plugin is dealing with Element Types.
BaseComponentModel is useful if your plugin is dealing with Component Types (tools, widgets, tasks, etc.). You can check the
craft/app/enums/ComponentType.php enum for a full list.
And BaseEntryRevisionModel is pretty self explanatory.
And there is nothing stopping you from extending things like Craft's own EntryModel directly, if you need specific features that it has.