Many folks are switching from wall-to-wall carpeting to hardwood floors and area rugs. You have to know what you're doing, however, because fiber is important in rugs. Here's how to select a good rug: Wool's best. It's beautiful tough and very costly. Nylon's good too, and costs much less. Ofefin's next on the totem pole and costs still less. Polyester is the least expensive. It's pretty, but doesn't wear well in high-traffic areas. With yarns, look for double twists for good wear. With orientals, more hand knots per square inch and ridges on the back that run parallel to the sides indicate better quality. And that's the On The House tip for today.