A good jersey top makes everything else in your wardrobe look slightly more expensive than it is, which is the main reason I own so many of them. There's no stiffness to fight, no ironing, just a layer that sits where you put it and gets on with the day.
Before you buy, check the weight of the fabric by scrunching a bit of it in your hand, because this tells you more than reading the label ever will. Thin jersey goes see through under light and clings in places you'd rather it didn't, and you only find that out properly once you're standing near a window at work wishing you'd worn a vest underneath. Look at the neckline and the hem too, because a boat neck sits differently on every body and a curved hem that looks nice folded on a shelf can ride up the second you sit down to eat lunch at your desk. A cheap jersey top looks fine for about three washes, then the neckline goes slack and starts gaping forward, and the whole thing takes on that slightly defeated look of something that's been through a tumble dryer one too many times. The good ones have a bit of weight and a bit of stretch recovery, meaning they spring back into shape rather than stretching out and staying there, and the seams are flat rather than overlocked thick enough to show through a fitted jacket. Run your thumb over the hem and the underarm seam in the shop if you can, because that's where the cheap ones fray first, usually around the second or third wash, which is sooner than you'd like for something you're going to wear weekly.
Where jersey tops let you down is anywhere that needs structure, so a formal office where everyone else is in tailoring, or anywhere you need the fabric to hold its own shape rather than yours. They're also not the answer if you run warm, because the better ones tend to be a bit heavier and don't breathe the way a cotton tee does. And they clash with anything else clingy or jersey based layered on top, a cardigan that's also knit and stretchy just doubles up the softness until you look like you're wearing pyjamas to the shop, which some days is the look, but not every day.
Worn under the blazer that's been hanging in your wardrobe since the last time you needed to look organised, a decent jersey top is what makes that blazer wearable on a Tuesday rather than only for interviews.