Which would you choose to use for..... Canon DPP (current edition) or ACR 3.7(CS2) via a conversion to DNG.
I sort of see advantages to both, but I do like the fact that ACR integrates with the whole Bridge/CS2 workflow BUT I wonder if there are quality issues to consider as well that I am not aware of rather than just personal choices over which product I prefer to work with.
(I know there are other choices inc. upgrading but for now those are my choices.)
There is a very simple answer to this question and that is....
With that said - you might like to consider that DPP provides only very basic adjustments compared to ACR. Out of the box, that is with all adjustments at default, you will get a better rendering from DPP. However, the moment you start twiddling the dials the game changes and the real power or ACR shines through.
I actually just noticed you specifically mention CS2... thats generations old now and my comments above relate to the current version of ACR. I assume you are limiting yourself to ACR3.7 version because you have it already and don't want to spend any money. I would rethink this approach if you are able. RAW processing has advanced considerably since ACR3.7. If your budget is tight then Adobe Lightroom is an excellent low cost alternative and gives you a really nice DAM tool as well. Another benefit of Lightroom - you dodge the entire CC storm.