Hi,
Where is the best day to spend Sunday? Rome or Orvieto?
thanks
Probably Rome since it's bigger and thus has more options. The Orvieto duomo might be tied up with services on Sunday mornings, but there are still plenty of places to wander.
The bigger problem is Monday. Some refer to Monday as blue Monday in Europe since this is the day that most public things are closed. Of course, there are exceptions but you are most likely to run into more closed sites on Monday than Sunday -- IF that is the question you were really asking.
Also -- see the responses under - Best day for Orvieto? - since that is very closely related to your question.