Which of the following treatments would be the be the best for treating dark knuckles?

There is no best treatment for this area and all the mentioned treatments (besides microderabrasion) are likely to help.  But this area is very genetic and due to sun and repetiative activity so I have never found anything that could clear this completely.  I suggest seeing an expert to get you on a series of treatments, sun protection and heliocare. An improvement should be anticipated, but cure is unlikely.  Best, Dr. Emer.

There are a few ways to go about it and it really depends on the look of your skin.You can try glycolic pads at home, nightly.  As well as urea cream 40% in the morning.