default shipping method

I've 3 shipping method; I want setup express courier as default shipping method, so when customer go to checkout_shipping page, the radio button is already cecked on express courier.
At this time is the store pickup shipping method already cecked.
Thank you

The default is the lowest price ...

Store Pickup would only be the default if that is cached as Store Pickup is coded to not default ...

To customize this you would need to change the shipping.php class and customize the code for:

      $cheapest = false;
      $size = sizeof($rates);
      for ($i=0; $i<$size; $i++) {
        if (is_array($cheapest)) {
          // never quote storepickup as lowest - needs to be configured in shipping module
          if ($rates[$i]['cost'] < $cheapest['cost'] and $rates[$i]['module'] != 'storepickup') {
            $cheapest = $rates[$i];
          }
        } else {
          if ($rates[$i]['module'] != 'storepickup') {
            $cheapest = $rates[$i];
          }
        }
      }

      return $cheapest;

Thank's a lot!
I've done:

  $cheapest = false;
      $size = sizeof($rates);
      for ($i=0; $i<$size; $i++) {
        if (is_array($cheapest)) {
          // never quote storepickup as lowest - needs to be configured in shipping module
          if ($rates[$i]['cost'] < $cheapest['cost'] and ($rates[$i]['module'] != 'storepickup') and ($rates[$i]['module'] != 'assegnato')) {
            $cheapest = $rates[$i];
          }
        } else {
          if ($rates[$i]['module'] != 'storepickup') {
            $cheapest = $rates[$i];
          }
        }
      }