How to separate Unit and Functional Tests in Symfony2?

I wonder :

1. if it's a good idea to separate tests (Unit | Functional ...) in Symfony2,
2. and how I should separate:

By folders structure :

tests 
|-- functional    
|-- unit

By config in phpunit.xml :

<testsuites>
    <testsuite name="unit">...</testsuite>
    <testsuite name="functional">...</testsuite>
</testsuites>

By annotation

/**
 * @group unit    
 */
 function testMyUnit()

Ii it a reasonable approach? Is there a standard way to do this? What "levels" separate (unit > integration > functional)? And how to take advantage of that if I want to play with these tests manually and fastest, and obtain rational coverage reports in Jenkins?