I would recommend you store it as an option
Here is the API:
add_option( $option, $value, $deprecated, $autoload );
update_option( $option, $new_value );
get_option( $option, $default );
delete_option( $option );
For your option I would not set autoload to true for performance reasons ( unless you are grabbing this option on every page ). I would also prefix every option name with a unique identifier e.g. 'MaltheMilthers_plugin_last_import'
Creating a dedicated table will mean writing SQL, and it means your plugin cant be used on hosts such as WordPress VIP or WP Engine.
In future you may also find these APIs useful:
- User meta
- Post meta ( and by conjunction attachments and nav menus )
- Comment meta
Though I wouldn't recommend them for this use case. Term/taxonomy meta is under discussion, and can be added via several plugins, though this also suffers from the same issue a dedicated table would have.