Which of these software would you use, or like using?

Within the PI canvas, only NoiseXTerminator is available to use within PI itself and it is fantastic.  While I do use Topaz DeNoise AI on images other than astrophotography, I no longer use it on deep space astrophotography images; I have used it on lunar and planet images occasionally.  I have found that any model of DeNoise is not-well suited for deep space astrophotography, particularly with star and background artifacts.  

Similarly, GradientXTerminator is only available for use within Photoshop, and before I learned PI, I did use GradientXTerminator somewhat effectively, though found that it often altered colors and luminance of DSOs or of more diffuse nebulosity.  I stopped using it after learning PI.  I have not used Graxpert, but have read recent good reviews as a stand alone program outside of PI and PS.  If you search the PI forum, you will read that there has been some discussions back and forth between PI developers and Graxpert developers, and it sounds as though Graxpert does a really nice job with gradients. Certainly, the price is right.

I would highly recommend Astronomy Tools from within Photoshop (https://www.prodigitalsoftware.com/AstronomyToolsActions.html). . Excellent banding reduction, deep space noise reduction, and improvements in star size/color/morphology if they look particularly "crunchy".  Noel Carboni has been very responsive to email support questions and even though I use Pixinsight for nearly all of my stacking and processing, I almost always take the "final" PI image into Photoshop as a 16 bit image and will tweak with Astronomy Tools and then with Camera Raw for final contrast adjustments.

I have not used DeNoise AI on astroimages for a couple of years, though use it all the time on conventional RAW images.

Good Luck and CS,

Rob

I use Siril or APP for gradient removal and background extraction and AstroDenoisePY for noise reduction. I use JR Macros in Affinity for any sharpening I may do later, usually just structure enhance. Why, they work and fit my modest budget. But, thanks to this thread, I will check out GraXpert although I think the latest BGE tools in Siril are based on the code from GraXpert.

Recently I started using GraXpert, the results are very close to DBE but it is more efficient to use. I had mixed results with SHO combined images, there the results were sometimes a bit strange so I use it on the uncombined images.
Another nice thing is the ability to convert files, I sometimes share my stacks with others so GraXpert is an easy tool to quickly convert xisf files to fits. And for those cases it is also nice to save a stretched version as a 16bit tif, then others can directly import the data into photoshop and have a good starting point for processing.

These days I use NoiseXterminator instead of DenoiseAI in preprocessing, it works better on large grain noise that I often see in the Sii channel. In rare cases where I do not have much data on Sii I use both to prepare that channel. Most of the time when I use DenoiseAI, I go for the 'Clear' result.

After I have finished processing I do a round of DenoiseAI, just to see if some areas are improved or not, when I see something I bring in the better places with a mask, when there is no or only little benefit I destroy the layer.