Sofa is the crucial element in any living room setting

SOFA, one of those lines,” she says.

Need to seat a large number of people comfortably?

“Sectionals deliver like nobody’s business,” she notes. In small spaces, they can seat enough people to avoid the need for extra chairs. In large spaces, they can fill space without looking awkward. And in awkward spaces, you can install a sectional with an interesting shape, like one with a curvy back.

Christie Leu, a designer in Chevy Chase, Md., also likes sectionals.

“They aren’t all L-shaped,” she points out. “You can get a pair of armless sofas and put a low table in the corner, or you can have a ‘bumper sectional’ in a narrow room that will still provide seating but not impede a view or weigh down a room with a heavy arm on one side.”

In choosing a sofa, consider how you will use the room, Leu says. Maybe you want to be able to converse easily, read and play games.

She’s a fan of single-bench cushions, so no one has to sit on a seam. And buy the best quality you can afford.

“As the price goes up, you’ll feel the difference between cushions and construction,” she says. “A cushion with good, hand-tied coil springs and high-density foam will last longer than all-foam, which will flatten in time.”

Leu doesn’t care for all-down seats “because no one has time to fluff them as often as they need it.”

Some other hallmarks of a well-built sofa: hard, solid woods and joints integrated into the frame.

For sofas that will see hard use, choose a hardy fabric, says Courtney Thomas, based in La Canada Flintridge, Calif.

“We use lots of polyester and chenille blends for sofas where large families put them to the test,” she says. “Generally, synthetics endure hardship better than natural fabrics, which don’t hold up as well.”

She says her firm often Teflon-coats fabrics for extra protection against stains and spills. She also likes Sunbrella upholstery; the outdoor-fabric technology has advanced so textiles are softer, and now well-suited for indoor use too.

Alison Pickart, an interior designer from Larkspur, Calif., advises against huge sofas.

“I don’t think you should ever have a sofa over 8 feet,” she says. “Very rarely will more than two people occupy a single piece of furniture. Plus, if your sofa is too big, the opportunity for other beautiful and interesting accent chairs, ottomans, poufs and small tables diminishes.”

To facilitate conversation, Pickart says, furniture should be arranged so that people are at 45 degree angles from each other.

“So the best living rooms are ones in which occasional seating can be comfortably placed at both ends of the sofa,” she says.

She also likes armless sofas in narrow rooms; using one or two center components of a sectional can be an option.

And don’t forget accessories, says Houston-based designer Margaret Naeve.

“I love to style sofas with oddly shaped pillows and a colorful throw to add something unexpected that also ties into other elements in the space,” she says.