The moment it clicked for me was a rental dining room with barely enough space to push a chair back without hitting the china cabinet. The table had been fine for years, but the chairs we'd picked for it were too deep, too wide, and every meal felt like a small negotiation about elbows. Swapping them for a slimmer set with no arms changed the whole room without moving a single wall.
Getting the size right starts before you buy anything, with a tape measure and a little patience. You want about two feet of width per person at the table, and at least two feet of clearance behind each chair so someone can get up without everyone else standing too. Measure the table height to the underside of the apron, then check the chair arms, if any, clear that line with room to spare, because nothing ages a dining room like a chair that bangs its elbows on the table every time someone sits down. Armless chairs are the forgiving choice for tight rooms and mixed seating, while chairs with arms look generous at the head of a longer table but eat space fast in a small one. As for materials, solid wood chairs, oak, walnut, ash, take daily life in stride, they get a little scuffed at the legs and a little softer at the edges with use, and that's not damage, that's just a chair being lived with. Upholstered seats are kinder on the back for long dinners but they show food and fingerprints faster than you'd expect, so a performance fabric or a leather that wipes clean earns its keep over a pale linen that looks beautiful for about three weeks. Where chairs fall short is in households with young kids and red sauce on heavy rotation, a fully upholstered chair in a light fabric is asking for trouble there, and a full set of identical formal chairs can make a casual, lived in dining room feel stiff rather than welcoming. For color and finish, I'd steer toward natural wood tones, black, or a soft neutral upholstery, they sit easily with whatever table and room you already have, and they don't date the way a trend color does. The one mistake to avoid is buying chairs that look right in a showroom photo but have never once been tested against your own table's height and your own room's walking space, because a chair that doesn't fit the table you actually own isn't a bargain, it's a daily annoyance you'll be living with for years.