To help you get a handle on it all, we spoke to Amy Archer, a consumer behaviourist with Rowe Furniture who also spent 10 years as a furniture designer. She knows her stuff and she's prepared to share.
The inner truth
A lot of what separates the good from the best in a sofa is happening inside. It's the things you can't see that really affect how well your furniture takes a beating (jumping, bouncing, being moved around). The starting point here is the suspension system.
These systems are modelled after the ones found in car seats, and the Cadillac of sofa spring systems used to be the "eight-way," something Amy describes as "a slinky with attitude": eight metal coils attached to each other and then to the frame with two metal ties. "Everyone used to say, if you want a great couch, you need an eight-way suspension system," says Amy. Not anymore.
Some great sofas still use this system, but when Mercedes introduced an "S system" for their car seats, this model made its way to the furniture showroom as well. (Think S-shaped coils running through the inside of the sofa and attached to the frame.)
The latest incarnation comes courtesy of Ferrari, which introduced a webbing system in its seats. "Henridone and other high-end sofas come with this new system," says Amy. "It's like super memory elastic, and the great thing is it never hurts the cushions, because whatever the spring system is made of, it pushes against the cushions." Any of these systems will give you longevity and durability.

4 Comments
How do I find a three-person sofa to fit down my basement stairs? The movers couldn't fit our last one in present basement. Any ideas? I live in Toronto.
It depends a bit on your stairs, but an option would be finding a sofa with modular construction. Some have backs that come off & arms that come off. The only way to find them is to find a helpful sales person who really knows the product or is willing to find out for you. We have a couple affordable options at GoWFB.ca.You can check them out here: http://www.gowfb.ca/Living-Room-Furniture-Sofa-Sets-c-10_40.php?cPath=10_40 Sincerely, Leah Galarosa, Wholesale Furniture Brokers, www.GoWFB.ca
Leah is right, modular sofas styles are the way to go when trying to fit pieces through tight spaces. W&C can customize a sofa for you as well, making it in peices so that it can fit down the stairs and then be put together once its in place. This way you don't have to have the look of a pieced together sectional or sofa look, we can customize it to look like one piece! www.whitewashco.ca/shop Jo Alcorn. support@whitewashco.ca All the best with your sofa search!
The new coils and webbing systems cannot compare with the comfort and durability of 8-way hand-tied springs for quality-built sofas. That is why all high-end upholsterers still use this system - it's still the best. If you want to ensure quality sofa construction, but from a store where you can actually see how the sofa is made - in Canada!