Both of the cymbals are medium-thin, so there is not a huge difference, but the sweet ride's ping is a little brighter so it should come through a little better than the K dark's. The dark ride will be a little easier to crash though when compared to the sweet ride because it's a tiny bit smaller cymbal, and the dark ride has a little less weight because of it. But one thing with Zildjian's rides especially, is that they tend to have a quite big scale of "acceptable" weights for a given cymbal. E.g. a quick youtube search shows K custom dark 22" rides ranging from 2410 grams to 2889 grams, and A sweet rides ranging from 2746 grams to 3025 grams. So you never know what kind of unit you're getting unless you can try them out in person or purchase from a place that sells the cymbals by weight. But the best thing to do is probably just listen through a ton of them, and getting an opinion which cymbal generally sounds better to your ears.
I'm currently playing an 23" A Custom 25th anniversary medium-thin ride (which is very similar to an A sweet ride, the A Custom just has a little smoother lathing and a brilliant finish on top), and it's by far my most favourite and most versatile ride cymbal I have played. It crashes easily, it's got a good wash but the stick definition still comes through, and the bell is bright and cutting. I played around with a 22" K Custom dark ride about a month ago, and it's ping was definitely a little darker when compared to my A custom 23", but it wasn't too far off.