I have both planing and sharpening videos from both authors
Very different. I think that DCs planing video taught me the most of all of them. I would go for this one for planing every time. Cosman's is very good, but DC is a real plane aficionado and you can tell from the vid. To see a man hand thickness wood to within a thou or two is quite stunning :shock:
DCs delivery is a little (too) slow at times whereas RC moves at a sprightly pace and so RC si more 'watchable'
Sharpening videos? Very different. If you want freehand sharpening then RC is not and you want to use a guide, then DC again. I personally would not pay for the sharpening videos with hindsight. DCs for instance taught me nothing I didn't already know, however, it was useful to actually SEE him doing it and compare to my own efforts. unlike the planing videos, I learnt nothing.
Best woodworking videos in my opinion? RC dovetails.