Hi,
I have asked previously around the difference between the two codecs, but have not had the oppertunity to use both untill now. The Samurai recording device we use has just received the latest firmware update, and it now supports DNxHD as well as ProRes. To date, I have been using the ProRes HQ format that the device allows - this gives a 10bit 22MB per second video recording (176mbps) - I shot a 10second clip today using the DNxHD codec, and see that it gives a 10bit 23MBper second video recording (184mbps). So the difference in file size and data rate is rather small (this was using DNxHD 220x codec). I installed the codec on my PC and am able to import both files. I do see a visible difference betrween the two though. The video recorded with DNxHD seems more "washed out" than ProRes. Ill add a screenshot below. both were shot under the same lighting - in fact the only time difference between the two, was the 10 seconds or so it took to change the device from ProRes to DNxHD.
I had the character slightly under exposed so that I could get the aperture a little smaller and more of the image in focus.
Is this the normal behaviour of the DNxHD codec? Since I have been working with After Effects, I have not run into any issues using ProRes, I am going to assume, untill I am corrected by the forum, that it seems to be the best codec for our current workflow for now 
Thank you
Pierre Devereux