education Spain secondary primary school

I'm interested in developing a CMS where to migrate my school web site. So far, I've tried Joomla and I was very satisfied with the look and the functions I was testing. But now I have just found this group who seem to be exclusively devoted to educational issues within Drupal.
I know, I know.. if you all are here that's because you already made your decision. But how could I be definitively convinced to make mine? Any objective criteria out there? What's for Drupal which is not for Joomla?

Thanks in advance.