A black top is the thing you reach for when you need to look like you've made an effort without actually making one. Under a blazer, over a skirt you haven't decided about, on a day when your brain's gone and you just need to get dressed and out the door. It's not glamorous work but it's constant work, and that's exactly why it's worth getting right.
The difference between a good one and a bad one is mostly in your hand before it's even on your body. Cheap black jersey has a sort of dead, flat feel to it, it doesn't move, and under certain lights it goes slightly grey or green depending on the dye batch, which is a miserable thing to discover standing next to another black top that's gone a completely different direction. A better one has some weight to it, a bit of give, it drapes instead of just hanging there like a bin bag with armholes. Seams sit flat, the hem doesn't curl up after one wash, and if there are buttons or a zip they feel solid, not like something that'll snap off by October.
Before you buy, check the neckline sits where it says it sits once you actually move your arms about, not just standing still in the changing room mirror. Hold it up to a window or a bright light, properly see-through black is common and not always obvious until you're stood under office lighting wondering why everyone's looking at you oddly. Check the fabric content too, a bit of elastane in a fitted one makes a real difference to how it survives a full day, while a stiffer cotton poplin wants to be worn a size up or it'll fight you every time you sit down.
It's not the right choice for everything, mind. A very thin, cheap jersey top is no good for anything that needs structure, it'll show every seam of whatever's underneath and cling in ways you didn't sign up for. And if you're after something that actually lifts an outfit, that does a bit of talking on its own, black is rarely the one doing that job. It's there to support, not to be the main event.
On shade, true black is the easiest thing in the world to live with, it goes with anything you own and doesn't argue with other colours the way a near black, slightly brown or blue toned version can when you put it next to something else black in the same outfit. A matte finish ages better than anything shiny or coated, which shows every crease and wear mark within a season.
Wash it inside out on a cool setting and skip the tumble dryer, it's the fastest way to stop black fading to that tired charcoal look after a few months.