I avoided modern stools for years because I kept picturing the ones with the chrome legs that wobble the second you lean on them wrong. What changed was a kitchen island in a rental that had no seating at all, and three stools that needed to tuck under it without looking like they belonged in a hospital waiting room.
Measuring is where most people get this wrong, and I did too the first time, buying a set that looked great in the listing and turned out to sit about four inches too low for the counter. You want ten to twelve inches between the seat and the underside of the counter or island, and you need to check the footprint of the base too, not just the seat height, because a lot of modern designs flare out at the bottom and will not slide under anything. If you're doing a run of three or more, measure the total width of the counter and divide by seats plus gaps, people need at least six inches of elbow room or dinner turns into a wrestling match. These suit kitchens and islands obviously, but they also do good work in a bathroom as a towel perch, by a console table in an entryway, or pulled up to a desk in a studio apartment where a proper chair would eat the room. They read best in homes that already lean a bit spare and clean, less so in a room full of turned wood legs and florals, where a slab seat and metal rod base will look like it wandered in from a different house. As for what separates the good from the bad, I flip every one of these over before I buy it, and the difference is obvious fast. A well made modern stool has a seat that's either solid wood or a properly finished plywood, not a thin plastic shell screwed onto a frame with four tiny bolts that will strip out within a year. The legs should bolt into actual threaded inserts in the seat, not just dig into soft chipboard, and welded metal bases should have clean, ground down joints, not blobby welds hiding under a coat of paint. A stool that's been through a real test, a spill, a year of kids climbing on it, a move where it got knocked around in the truck, should still sit flat on the floor with no wobble and no cracking at the base. Cheap ones loosen at the leg joints within months and start creaking like an old staircase.
The ones I keep coming back to have a seat edge that's been eased just enough that it doesn't dig into the back of your thighs after twenty minutes, which sounds small until you're the one sitting there through a long dinner.