Generally, the rounder the arm, the more traditional the sofa. For a modern pick that’s also pretty timeless, try a tuxedo-style sofa, which has straight arms the same height as the sofa’s back, says designer Elaine Griffin. “It’s the LBD of upholstered seating—it meshes well with any style of room.”

To Buy: Carroway sofa, from $1,400; shopsocietysocial.com.

Think about your intentions for the space. If it’s more of a formal living room—a stylish spot for occasional entertaining—you’re better off with a stand-alone sofa, which has a sleeker, cleaner line. A sectional is so roomy and inviting that it tends to scream casual (great for lounging, watching TV, napping, or playing games around the coffee table).

“Cotton velvet is essentially no-fail. It’s plush and wears well,” says designer Young Huh. “Go with a stain-camouflaging pattern in a dark color if you don’t want a ‘no eating on the couch’ rule in your house.” Avoid chenille, which stretches and warps over time.