It really depends on the requirements of the project. Drupal remains our number one weapon of choice and we have been able to implement cost-effective but highly professional e-commerce solutions using Drupal for many years now. We have also implemented pure PHP e-commerce solutions and a variety of e-commerce solutions using popular frameworks like Zend and Laravel.
When we decide on the best solution for clients, it is only after we have done a thorough analysis of the needs of our clients. We don't believe in one-size-fits-all solutions, but we have found that in most cases, if selling online is the goal, a combination of Drupal and well-programmed custom modules can go a very long way in delivering a robust and scalable solution.