D5 has higher flow, best for low restriction loops; DDC higher head pressures, best for high restriction loops. The top argument is quite pointless, because you can change the D5 top to a higher performance top as well, and plus you can run D5 at 24V with a step-up pump controller, which beats any DDC with aftermarket top, bar none.
Oh, and I don't understand why people say the DDC is noisy. I had mine at almost 5000 RPM and I couldn't even hear it. But it does run very hot. Some people install a heatsink on it.
All you need to do is run it on 24V if you get a D5/S. Even with stock top a 24V D5 blows the DDC out of the water by a big margin.
As for the noise of the DDC, I used the XPSC reservoir top and honestly didn't hear any noise even with my ear next to the case. Maybe it's noisier with the stock stop, I don't know. To me heat is a bigger issue with the DDC's than noise, and some airflow goes a long way.