4 single sites VS multisite wordpress

You can use one installation for four (or more) singular sites without multi-site. Just point all domains to the same directory with your WordPress installation. In your wp-config.php set the necessary variables and constants depending on the currently requested host:

switch ( $_SERVER['HTTP_HOST'] )
{
    case 'example.com':
        $table_prefix   = 'ecom_';
        $table_name="ecom";
        break;

    case 'example.net':
        $table_prefix = 'enet_';
        $table_name="enet";
        break;
    default:
        $table_prefix  = 'wp_';
        $table_name="wp";
}

You can change any constant or variable in the switch of course.

To make plugin updates easier let all installations share one plugin directory.