Our stay at Tuco Hostel was really good! First the hospedaje is well-situaded, not far from the centre of Cusco but not in a touristic area, which is nice. Then the hostel is great, with nice rooms (our room was big and its price was cheap!), common areas, kitchen etc... Finally, the staff is nice and Coco, the owner, is really helpful providing a lot of precious advices.
The only thing : don't do the touristic bus trip between Cusco and Puno (Coco might propose to you), it's a rip-off!! Just go with a regular company.
If I have to come back to Cusco, I'll go back to El Tuco, for sure!