At Spade and Archer Design Agency we almost always hang artwork above the sofa if we can.
Note, sometimes there is a window or no wall behind the sofa, thus art would not work there. There are a few rules here. We use a piece, or pieces of art that combined are, at least 50% as visually large as the sofa but no more than 100% as large as the sofa. In this shot we can see the artwork is about 75% as large as the sofa. We center the artwork on the sofa, and hang the artwork about 4” above the back of the sofa to the bottom of the artwork. Note, 4 inches about the size of your fist from the pinky to the thumb.