I ran some recent tests using Topaz Reduce Noise, AI Clear, Photo Ninja Noise Ninja 4 and Topaz Denoise 6. AI clear was used in the auto mode for the initial run. The test image was a 12800 ISO jpg. For this, NN4 edged out AI Clear because of the color splotches Clear left behind. When AI Clear was changed to High it tied or slightly beat NN4.
Original Sony A55 image:
Noise Ninja 4 result:
Topaz Denoise 6 (older plugin):
AI Clear high:
I then went into Topaz Studio to create a preset that might work even better but using Topaz AI Clear. Using downloaded test files from a Canon 80D (I only have a Sony camera) with ISOs of 200, 3200, 6400 and 12800 I ran tests of my preset.
The ISO 200 was a reference to see If low noise pictures could still benefit since AI Clear also does other functions like sharpen. The results below are a 100% enlarged section of the downloaded shots with the Perfect denoise preset applied. No adjustment was made to the preset, all ISOs had the same adjustment.
Whole image ISO 12800 after Perfect denoise preset::
I have reduced the image size to make a TSP file using the whole image. This will allow you to open in Topaz Studio and then save the preset. I found that you don't need to adjust anything at least up to 12800, its automatic. It's in my Dropbox for download. https://www.dropbox.com/s/316qiioskd279wd/12800_ACR%20-%20Perfect%20denoise%20RL.tsp?dl=0
The original 6000 x 4000 px test images with noise may be found here: https://www.imaging-resource.com/PRODS/canon-80d/canon-80dHI_ISO_NR.HTM Notice that for each ISO there are 3 images, one with noise reduction (skip), one with NR off and the one on the right is Adobe Camera Raw with no noise reduction (use this one for high ISO).