“Quality sofas should feel solid and heavy. Flop around on one to test its sturdiness, then lift it up by the corner and shake it a bit. If it feels light or wobbly, take a pass. Look for a frame made from a kiln-dried hardwood such as oak, alder, birch, maple or, alternatively, high-quality hardwood plywood or marine plywood. Eight-way, hand-tied springs are a hallmark of fine furniture, but sinuous S-shaped springs can provide nearly as much comfort. Drop-in coil springs are a less costly alternative.
Most cushions have a core of polyurethane foam; the denser the foam, the heavier it is and the longer it will last. In the cheapest furniture, the cushion is filled with just the polyurethane foam core. In better furniture the core is wrapped with Dacron batting. Higher-quality options include poly-down cushions, which have down mixed with the batting; spring-down cushions, which feature a core of springs surrounded by foam and feathers; and all down, which is all feathers (and all work, so avoid this unless you have servants).
The best sofas have joints that are double doweled and fitted with corner blocks that are both glued and screwed (not stapled) into place. Quality pieces have legs that are part of the frame, not just attached to it (although removable feet do make it easier to get items through doorways).
If you’re short on space, think about buying a sofa with low arms or no arms — it’ll make your room look larger.
As a rule, synthetic fabrics are more durable, colorfast and cleanable. Tightly woven fabrics and fabrics that are heavy will stand up to wear and tear better, as will leather. Avoid satins, brocades and damasks unless the sofa won’t get much use.”