I have DeNoise Ai, Sharpen AI, JPEG-to-RAW AI, Gigapixel AI, and (recently) Mask AI. I have used Sharpen and DeNoise for almost a year now and I would say that I use DeNoise about 85-90% of the time and Sharpen the other 10-15%. I really like that Topaz Labs has had several updates of both in the past year, and each update seems to make the programs a little better.
As mentioned by others here, Sharpen has some deNoise features, and DeNoise has some sharpening features. Since I photograph primarily birds, and Birds-in-Flight (BIF) with a D500 & Nikkor 200-500mm lens, I find that noise is the biggest issue. Especially at this time of year when we have fewer hours of daylight and I tend to shoot closer to "roosting" time in the mid-to late afternoon. Also, in the past 2 months, we've had a lot of cloudy days here in NJ which also cuts down on the light. Although I have my D500's maximum ISO set for 8,000 (deliberately to minimize noise) I still often want to "smooth out" the shot and DeNoise AI does a beautiful job!
DeNoise has 3 "Ai modes": DeNoise AI, AI Clear, and Low Light. Generally, I preview my photo using each and see which one looks best, and then do fine-tuning with the "Remove Noise" and "Enhance Sharpness" controls. Most times, this gives me the type of image that I'm looking for.
I have a growing appreciation for Sharpen Ai now, especially with distant birds, small songbirds, and BIF. Its 3 "AI Modes" are "Sharpen," Stabilize," and "Focus." I was amazed when I first started trying Stabilize and Focus modes. Initially, you might think that Sharpen is all that you need, but when I tried each, one after the other, I found that more often than not, it was Focus or Stabilize that my image REALLY needed! (And since I do all of my shooting handheld, these two modes are VERY useful.) Similar to DeNoise AI, there is a "Noise Suppression" and "Sharpness" control for fine-tuning, and some other controls that I haven't tried yet.
I should add that when using "Sharpen" mode you need to be aware and careful of the "Jaggies" that can occur in what would normally be smooth, straight lines; and also the white halo that I have noticed that can start to appear around objects if you sharpen too much!
Previewing each modes' results, I find to be very quick (i.e., about 3 seconds), BUT I have a 2019, 27" iMac with a 3.6 GHz i9 (8-core) processor, 24 GB RAM, a Radeon Pro Vega 48 graphics card with 8 GB of VRAM, and a 2 TB SSD. If you have a computer with lower specs, as mentioned above, you will probably have to wait longer to see each mode's preview results.
BOTTOM LINE: Topaz DeNoise AI AND Sharpen AI are two software tools that I think EVERY photographer should have in their toolbox!