My goal is that there is only one setting, which would be called something like “Preserve Details”. If the denoiser would have some uncertainty how to denoise some pixels, you could be able to decide on those whether they should be blurred or if you prefer to have some noise. Have a look at the video on this page (“Preserve Details” would be what they call “Lambda”):
It would be ideal to have the denoiser as a node in the compositor. This would give the user most freedom and give access to all passes and the user might even choose whether the noisy or denoised passes should be used.