Area rugs and runners are usually laid where the bulk of the foot traffic is. (That's human feet.) AT worst, this type of carpeting will keep the scratches to the perimeter of hallways and rooms.
If you do lay down carpeting, make sure you use carpeting with foam backs or stand-alone foam padding. The stores that sell both hardwood floors and carpet will know about this if you mention it to them. (Don't count on them bringing up the 'special' foam backing.) If you don't do this, your carpeting WILL leave worst scratches and damage than your pets will! And you'll certainly do a lot of slipping too w/o the foam.