Which is the better screen to land on after adding an item to a data list?
Depends on the context in which your users will be using this feature.
If you know they will be adding items frequently, or specifically, in large batches at a time, remaining on the add item page is more convenient. If adding an item is something that happens once and a while during normal use, then I believe the expected behavior is the redirection to the updated list of items.
If you haven't already, speak with your users to understand the usage of this feature, and more upfront, ask them what they expect to happen.
Jira has an excellent approach to this when creating new tickets (work items). There is a check box at the bottom of the form that says "create another" If the box is checked the user sees the second version with a small dialog that confirms the item was created and the form is cleared. If not checked the user goes back to the previous page (and if that was the list the item would appear in the list with a dialog box that confirms to the user it was created).