It depends On what you are trying to carve/mill with your tool. To give an idea of what kind of power the dewalt is it is 600W.
The whole thing started with a foredom style knock off, that was 350W if I remember correctly. So I would try and get above that, then pay attention to run out and collet size.
There is not a one size fits all. If you are just carving foam -a cheap rotary tool is plenty, milling aluminum -500W+.