Hold them up against your actual ankle before you decide anything. Cropped jeans live or die on where they stop, and that point changes depending on your height, so the length that looked perfect on the model is not a promise. The best ones hit somewhere between the slimmest bit of your calf and just above the ankle bone, and they should do it without clinging there like a tourniquet.
Mid blue and a worn, slightly faded indigo are the easiest shades to actually wear, because they go with nearly everything and don't shout about being new. A soft black is useful too, though it fades to grey faster than you'd like and never quite recovers. White cropped jeans are lovely for about three wears and then you remember you own a kitchen, a dog, and a bicycle, and the white remembers too.
They don't sit well with anything long and floaty on top. A maxi cardigan or a long tunic over cropped jeans just cancels the whole point of the crop, you end up with fabric bunching exactly where you wanted ankle to show. Chunky lace up boots can fight the hem as well, especially if the jean is slim through the leg, you get a strange stop start look rather than a clean line. Heavy knit socks peeking out doesn't help anyone.
Be honest about when they're the wrong call. If you're tall through the leg, a crop can read as "jeans that shrank" rather than a style choice, and you may need a pair cut specifically longer in the rise to balance it. In proper cold weather they leave a stretch of bare ankle that no amount of good humour makes warmer, so they're a three season jean at best for most of us. And if you want something to wear with heels for a smarter evening, a crop can cut the leg at an odd point, a full length or a slim ankle grazer usually does that job with less fuss.
A stretch denim with a bit of elastane in it moves well through a day of sitting and standing and holds its shape longer than you'd expect, though it does go slightly baggy at the knee by evening before springing back after a wash. Rigid cotton denim ages better over months, it softens and moulds to you rather than stretching out, but it takes longer to feel comfortable in the first place. Wash them inside out, on a cool cycle, and skip the tumble dryer if you want the hem to stay a hem rather than a fraying question mark.
Reach for them on the days when you want to look like you've made an effort without actually wearing anything restrictive, trainers or flats, nothing fussy on top.