Buying large pieces of upholstered furniture, such as a sofa or easy chair, can be a success if you can separate quality furniture from the stuff that just looks good on the surface.
At the heart of it all is the frame. If a piece of upholstered furniture doesn't have a good frame, it doesn't matter much what the rest of it is like. It won't last that long and won't provide you with the comfort you deserve.
For many years, the best frames have been made of kiln-dried hardwood. Its chief asset is that it won't warp. Today, though, you may also find top-quality furniture frames made of steel and even hardened plastic. Traditional furniture dealers still look on kiln-dried hardwood as the best, though.
Spring construction is another big factor. Coils that are hand-tied eight ways are considered the best. Lagging not far behind in quality is furniture made using the drop-in coil.
The next determining factor is the quality of the cushions, specifically, the density and material that goes inside the cushions. The best furniture has a density rated at 2. You can still get good cushions with a density rating of 1.5.
The material that goes into the cushions? That's all over the map these days. One good choice might be something that has polyurethane foam with a polydacron wrap and sewn into a muslin bag. You'll also find some good cushions that have a polyurethane foam wrapped in Dacron. But there are many others to choose from and you should certainly go by what feels good to you as well.
As to the exterior of upholstered furniture, it's hard to say one type is better than another because how the furniture will be used is a major factor.
For instance, if you have children and a pretty active household but you insist on fabric, you may want to consider something that is made with a durable fabric in a tight weave. Perhaps something with polypropylene or nylon. If the kids are grown and you're mostly entertaining adults, perhaps something in damask or a brocade, materials that don't stand up to a beating but look good.
If you have pets, leather is durable and looks great.