We stayed at the Palazzo Piccolomini in Orvieto last year.  This year we stayed at La Badia which is located in an old abby.  The Palazzo Piccolomini has a new and old building so you need to decide which one suits you.  We have stayed in both and both have advantages and disadvantages.   The Piccolomini is in a great location witin walking distance of lots of restaurants and basically near everything you could want to do in Orvieto.  Both times we stayed there our rooms were clean and sufficient.  The staff has always been helpful.

http://www.hotelpiccolomini.it/

La Badia di Orvieto is a wonderful hotel located in a restored medieval abby.  The grounds and views are beautiful.  I know you here it often when people talk about Italy but it really was like stepping back in time. 

As with all trips the room is key.  Make sure you ask in advance for a large view with a room.  Our room was basic but comfortable and clean.  Since this is a converted monestary not all rooms are the same and from what I heard from other guests some were very uncomfortable.   

Breakfast is served in the refrectory and was sufficient for us.  We enjoyed the fresh fruit, yogurt and pastries.  Scrambled eggs were available, but you had to request them.

 There is a beautiful pool area - it was too cool to enjoy when we were there but I can imagine it would be great when it is hot. 

We enjoyed spending several evenings on the terrace drinking a glass of wine and looking at the surrounding olve trees and vineyards