A good wide leg jumpsuit has weight to it. Pick it up and the fabric should drop rather than float, enough body in it that you can tell, just from holding it against yourself in the mirror, that it's going to fall in a straight line from hip to ankle rather than cling anywhere. If it feels thin and slippery in your hands, be wary. That's usually the one that looks brilliant on the hanger and does something unfortunate the second you sit down.
It's not for everyone and not for every day, and I'll say that plainly because nobody else selling you one will. If you're under five foot four and the leg isn't cropped or the waist isn't high, you can lose your whole shape in it, legs gone, middle gone, just a column of fabric with a head on top. Stairs with a drink in your hand are a genuine hazard, I've trodden on my own hem walking up a single step and gone down like I'd been shot. And anything with a fitted waistband worn after a big lunch is asking for trouble, there's no give, you just have to sit there radiating quiet regret until the bread settles.
Where it earns its stripes is in how little fuss it needs once you've got the fit right. A decent one, proper fabric, doesn't crease into a disaster the way a flimsy one does, you can pull it out of a bag after a few hours scrunched up and it mostly drops itself back out. Wash it less than you think you need to, cold, inside out, and skip the tumble dryer entirely because that's how the leg shrinks up and suddenly you've got cropped trousers you didn't ask for. Hang it rather than fold it if you can, the weight of the fabric does half the ironing for you overnight.
Colour wise, I'd go for the ones that don't shout. A proper dark navy or a soft black feels like trousers you already own, just better behaved, and goes under a plain shirt or a jumper you'd wear with anything else. Stone and olive are forgiving too, they hide travel creases and don't show every bit of dust off a train seat. Save the bright colours and bold prints for when you actually feel like being looked at, because in strong colour the whole outfit becomes about the jumpsuit, there's no hiding in the corner of a room in head to toe orange.
When you're next looking at one, check the waist sits properly on its own before you even think about the leg, because a loose waist ruins everything underneath it.