Magento : Fastest way to update a product attribute

Question

I'm looking for the fastest and reliable method for mass attribute update. Below are the methods am aware of but I don't know with which I should go.

$store_id = 0;
Mage::getSingleton('catalog/product_action')->updateAttributes(
    array($product_id),
    array('attribute_code' => $attribute_code),
    $store_id
);

or

$product->setData($attribute_code, 1234); 
$product->getResource()->saveAttribute($product, $attribute_code);