I found a quite simple solution for my question:
Adding a parameter to the route of registration:
<route id="fos_user_registration_register" pattern="/{utype}">
<default key="_controller">FOSUserBundle:Registration:register</default>
<default key="utype"></default>
</route>
So in the controller I could use this parameter in a condition to decide which type of registration I need:
//.....
$regtype = $request->get('utype');
if ($regtype ==='candidate')
$type = 'candidateform';
if ($regtype ==='company')
$type = 'companyform';
if (!empty($type))
$formFactory->setType($type);
//.....
if ($form->isValid()) {
//....
if ($regtype === 'candidate'){
//...
}
if ($regtype === 'company'){
//..
}
In this way I can control the form rendering, also the action.