I spent a long time thinking modern meant cold, all hard edges and chrome, something you'd find in a waiting room rather than a kitchen. What changed my mind was sitting in a molded chair with a bit of give in the shell and realizing it wasn't about looking severe at all, it was about getting rid of everything a chair doesn't need.
The good ones age better than you'd expect. A plastic or resin shell doesn't crack or fade much if you keep it out of direct sun for years on end, though I've got one by a window that's gone a shade paler than its twin and I've made peace with it. Wood legs want an occasional wipe with a damp cloth and nothing acidic, and if they're the oiled kind rather than lacquered, a little furniture oil once a year keeps them from drying out and going gray at the joints. Upholstered seats show their age fastest, crumbs in the seams, a worn patch where everyone's hands land getting up, so anything with a removable cover is worth the extra searching. Metal legs scuff if you drag the chair across tile, so felt pads aren't optional, they're the whole point.
In an ordinary room these chairs do their best work mixed in rather than matched up. A set of four identical ones around a table can feel like a showroom, but two modern chairs pulled up to an older wood table, or one bold one next to a plain bench, reads like someone with actual taste rather than a catalog. They sit well against warm wood floors and plain walls, and they're forgiving of a room that's otherwise a bit mismatched, since the clean lines give your eye somewhere to land. Where they struggle is next to a lot of other fussy, ornate furniture, they just look like they wandered in from another house.
Check the underside before you buy, run a hand along where the seat meets the legs, there shouldn't be any wobble or a seam that catches on your palm. Sit down harder than feels polite. A well made chair takes that weight without a creak, a cheap one announces itself immediately with a crack or a shift you can feel through your spine. On delivery day, check the legs are actually level on your floor, not just the showroom's, and look at the finish in daylight rather than store lighting, plenty of gray looks blue under fluorescents.
The real pleasure is a chair that sounds solid when you pull it out, a short, confident scrape rather than a scrape and a wobble, every single time you sit down to eat.