In my point of view the magento is only best plateform for E-commerce site and is more secure and shows a good performance and their benefits are,
1. High availability: Retain existing customer
2. Scalability: Add the number of new customers
3. Central management: Better support to the customers
4. Enable opcode cache, for example APC or Zend Guard this will increase load speed of php.
5. New releases often include performance improvements and other patches which affects performance.
As for me both solutions are rather complicated but extremely powerful. It really worth to spend some time to learn both of them.
However, Drupal is not that good for ecommerce as Magento. Ubercart and Drupal commerce are quite solid solutions but still Magento has more features, more extensions, etc. Here is a nice comparison of both platforms.
Personally I would suggest to combine Magento and Drupal. It will give you both ecommerce and cms features.
Here is a nice free extension that does this job
http://www.shopping-cart-migration.com/blog/42-magento/6189-unlimited-business-growth-magento-or-drupal
