To achieve the "Best" result, do not just apply it once with default settings. Follow this workflow:
This determines how aggressively the plugin looks for actual signal (galaxies/nebulae) versus noise. gradientxterminator113 serial fff21 best
To get the "best" results mentioned in your query, you must prepare the image correctly. GXT works mathematically; if the data isn't right, the gradient removal will fail or create artifacts. To achieve the "Best" result, do not just