The choice of whether to use omeka.org or omeka.net for your project will depend on your project goals. Make sure to discuss both options with your librarian to determine which is right for you BEFORE beginning your project.
Omeka.org
Pros:
-Free and robust
-Highly customizable
-No storage cap
Cons:
-Difficult to manage & make changes
-Maintenance requires attention
Omeka.net
Pros:
-Pricing models give you more flexibility
-Easy to manage
-Easy to update and maintain (Omeka updates the site for you as updated versions of the software are released)
Cons:
-Appearance and functionality relatively limited
-Storage cap makes certain kinds of content difficult to work with (large video and audio files)