This question is very similar to one that I have answered recently, so here goes...
Eagleton has a surprising and novel "take" on the witches in Macbeth. He argues that "the positive value of Macbeth lies with the three witches" and the witches come out of the play as the heroines, because they "expose a reverence for heirarchical social order for what it is." He argues they have their own sisterly community which lies on the "shadowy borderlands" of social order. Although he does not fully explain his justification for calling them the "heroines" of the piece, it is clear that the witches, in their sororial community, stand in opposition to Macbeth and his self-obsessed lust for power and position. The witches then could be argued to be the repressed subconscious of the play, who by releasing ambitious thoughts in Macbeth, show social order and heirarchy to be based on nothing more than "routine oppression and obsessive warfare". This view plunges the witches into the role of truth tellers, exposing power for what it is.
It is interesting that this view runs counter to the main view that is held of the witches: that they are manifestations of evil in the world and whose purpose is to tempt and torment people by offering vague and nebulous promises of supposed possible futures. They appeal to our desire to control our future and be actors of our own destiny. Of course, that future never happens in the way we want it to.
As to the comparison of both views, I think both have their own merits and truths. Undoubtedly we would be wrong to side with Eagleton and ignore the witches as a facet of evil in the world, but at the same time, Eagleton makes a very interesting point about the nature of social order with his critique of the witches.