On the six K bikes I've owned the past 6 years I've had two Fox twin clickers, three Works Performance(now Worx), and a YSS.
Of the three different brands, in my opinion the Twin Clicker when dialed in is the nicest for a plush ride and good control. I had one on my first 16V K100RS and now have another on my K100RS SE. Unfortunately they aren't made anymore and used units are getting pretty scarce. My only complaint is that with all the preload and damping settings, it's really easy to get it set up wrong. It took a whole summer of fiddling to finally get it dialed in. Even though they are out of production, there is at least one outfit selling rebuild kits and servicing them.
The next is the Works Performance(Worx) that I have had on my K75's, the RT and my K75S. Both had the three stage spring unit. These shocks are pretty easy to set up, if they built it for you all you have to do is put it on the bike. There is a lever that lets you set how much travel you get in the lightest spring before switching over to the next heavier of the three springs. Basically, switching that transition is how you adjust for heavier or lighter loads on the bike. It works pretty well. The ride on my K75RT is plush but controlled, it makes it easy to do up to 14 hour days when I'm trying to cover a lot of ground. They are still made, and you can get them serviced pretty reasonably. If I recall, I had the one on my K75S rebuilt and the length changed for a bit over $100. Length is adjusted by installing a spacer inside the body on the rod. Makes changing length pretty easy when doing a rebuild. I bought a seal kit and rebuilt the one on my K75RT at home. Was pretty easy, all I needed was a spring compressor for special tools.
The YSS is sort of a johnny-come-lately and I've only had it on my latest 16V K100RS for a bit over a year. It has a single spring with adjustable preload and rebound damping adjustment. So far, I really like the way the bike feels and handles with it. They are "custom" built for your weight, bike, and riding style. They are also one of the least expensive aftermarket shocks you can get for a brick.
Bottom line is that I wouldn't hesitate recommending any one of the three for a K bike. If you can do a rebuild, the Fox and the Works can still be had reasonably on ebay from time to time. For a new shock the Worx or YSS are good choices. The YSS is a little less expensive than the Worx if you are on a budget.
There are others out there, but I have a hard time with putting a $900+ shock on a $2000 bike. I'm just not able to justify that price for a 30 year old bike. If the handling at high speed is that important to you, you should probably be riding a modern bike, not a brick.