http://www.mahoodsculpture.com/the-pieta-sculpture/

Which “Pieta” is better? The one by Giotto which is a fresco or the sculpture by michelangelo?
It depends on what you mean by “better”.
Better at elliciting feeling?
Better to study?
Better at portraying a particular scene?
Better at influencing subsequent European art?
They cannot be compared on such a broad criterion. One is a sculpture and the other a fresco – one is much older than the other. One is colourful, zesty and ahead of its time. The other is quiet, subtle and stunning.
To make a valid comparison, you must compare equal things.
Giotto’s colourful fresco is full of movement. Even the stars overhead seem to be milling around in sympathy. On closer scrutiny, they turn out to be angels! A number of characters surround the Madonna an her dead Son – they need to be studied too. Bodies lean forward, the movement is amazing for such an early work. The sculptural rocks and hills divide the picture into an unusual perspective. We have to think as well as look.
Michelangelo’s sculpture is static, still and contemplative. Nothing distracts us from viewing the two memorable faces, one of which is turned away, which makes US move around to view it better. The folds of robe are perfect, the slight tilt of the Madonna’s shoulders so magically engaging. One of her hands is upturned, and speaks volumes, even though her face seems placid. There are no carved creases in her brow, and yet we see them.
Two works capable of raising the viewer’s awareness that there’s more to art than just depiction.
What does each do to the viewer? Are the feelings based on observation that is comparable in any way?
There are many Pietas in the world of art. To examine them and analyse them in a valid way, we have to find a criterion that will validate one aspect of their importance at a time. Then we will be able to assess how these aspects have become so significant.
I hope this helps.
Father Joseph Johnson discusses the Pieta, Part 1