Please vote!

preferred-namespaces-syntax.php

a) Importing the namespace only

    <?php
    use Symfony\Component\Form
    
    class ContactForm extends Form\Form
    {
        protected function configure()
        {
            $this->add(new Form\TextField('subject', array(
                'max_length' => 100,
            )));
            $this->add(new Form\TextareaField('message'));
            $this->add(new Form\EmailField('sender'));
            $this->add(new Form\CheckboxField('ccmyself', array(
                'required' => false,
            )));
        }
    }
    ?>

b) Importing all classes separately 

    <?php
    use Symfony\Component\Form\Form
    use Symfony\Component\Form\TextField
    use Symfony\Component\Form\TextareaField
    use Symfony\Component\Form\EmailField
    use Symfony\Component\Form\CheckboxField
    
    class ContactForm extends Form
    {
        protected function configure()
        {
            $this->add(new TextField('subject', array(
                'max_length' => 100,
            )));
            $this->add(new TextareaField('message'));
            $this->add(new EmailField('sender'));
            $this->add(new CheckboxField('ccmyself', array(
                'required' => false,
            )));
        }
    }
    ?>

a) is more conscise, and when building form we add, remove field so namespaces may increase as we forgot to remove unused one