The real tell with a card holder isn't how it looks on day one, it's what the card slots look like after a few months of being shoved in and out at the self checkout. Cheap ones stretch and go baggy, so your cards start sliding about or falling out when you open it on a bus. Good ones stay snug for years, which is a strange thing to be grateful for, but you will be.
If you've got none of these and you're starting from scratch, go for the simplest version you can find, something with four or five slots and nothing fussy, no extra zip pocket for coins, no fold out bit for cash you'll never use. You want it to replace a big purse, not become a smaller version of one. A plain rectangular holder that fits in a coat pocket or the front of a bag does more for your daily life than anything with extra features, because the extra features are usually the first thing to wear out anyway.
What separates a well made one from a disappointing one comes down to three things, and you can check all of them in the shop. First, the leather or fabric itself, if you pinch it and it feels thin and papery, it'll crease and crack along the fold line within months, you want something with a bit of body to it. Second, the stitching around the card slots, uneven or loose stitching there means the slots will loosen fast, run your finger along the edge and see if it catches. Third, any popper or clasp, cheap metal ones tarnish and stop closing properly embarrassingly quickly, so give it a few clicks in the shop and see if it already feels gritty. A good one will have none of that, it'll feel tight and slightly stiff when it's new, which is exactly what you want, not floppy.
Also worth a proper look before you buy, how many cards actually fit without the thing bulging like it's swallowed a small brick. Slot your own cards in if you can, three is fine on paper but feels different in a pocket than five does. As for what it goes with, it's one of those things that quietly sorts out your whole bag situation, it sits in a coat pocket on a day you're not carrying a bag at all, it goes inside a tote with your keys and lip balm when you want to travel light, and it works just as well tucked into a cross body bag for an evening when a full purse would be overkill. It pairs with everything because it asks nothing of anything else.