I have been reading up on the differences and while it is rather vague, the main difference seems to be that:
Drupal is better for larger sites and is easier to add onto or extend.
Drupal has better documentation.
Joomla seems to be better for newbies where Drupal is more for the web developers (so it wouldn’t work for too well for churches.
Drupal has the ability to add custom fields where I am still trying to find a work around in Joomla.
I have also read that the ecommerce component is better in drupal and has better support.
Need a very very simple site, then use WordPress, but it is limiting and you need to pick the template that fits your needs and style. You will find the cost to be from free to $100 for the template of your choice.